On Ed, Edd n Eddy, Lee Kanker and Sarah have Janyse Jaud as their voice actor. Marie Kanker and Kevin have Kathleen Barr voicing for them. And May Kanker and Nazz have Erin Fitzgerald as their voice actor.
Most of the cast of hundreds are voiced by about a dozen people. Yeardley Smith (Lisa) and Marcia Wallace (Edna Krabappel) are the only ones with a single regular character (though Yeardley Smith has voiced girls who were similar in personality to Lisa, such as the island girl in "Missionary Impossible" that Homer named Lisa, Jr. and Lisabella from "Last Tap Dance in Springfield.") This trope plays out most often with Mr. Burns and Smithers, who interact in almost every episode that contains either of them, and who are both voiced by Harry Shearer (making the Ho Yay between them a strange case of Screw Yourself).
The Simpsons also called attention to this trope in "The Itchy and Scratchy and Poochie Show", where the same voice actress was revealed to do the voices of both Itchy and Scratchy (which she demonstrated for Homer).
Other examples include Dan Castellaneta as Homer Simpson, Grampa Simpson, Barney Gumble, Groundskeeper Willie, Mayor "Diamond" Joe Quimby, the Mexican bumblebee man, Arnie Pie (the hapless helicopter pilot who hates Kent Brockman), the Squeaky-Voiced Teen (real name: Jeremy Freedman), and the Crazy Old Jewish man; Julie Kavner as Marge Simpson and all the women on Marge's side of the family (twin sisters Patty and Selma, her mom Jackie, her Great Aunt Gladys from "Selma's Choice," and an unnamed grandmother in "Fear of Flying"); and Nancy Cartwright as Bart Simpson, Ralph Wiggum, Todd Flanders, Lewis (one of Bart's friends from the early seasons. He was a black kid with a grayish-black afro), Nelson Muntz, and Kearney Zzyzwicz (the bald bully who looks like a teenager, but isn't).
On Beast Wars, Scott McNeil was often found arguing with himself as Rattrap and Dinobot. (And the entire Golden Disk talk between Waspinator and Dinobot, and the issues Rattrap has with Silverbolt...) He also does a large chunk of each cast he's a part of, in anime dubs, American cartoons and video games. In a Gundam video game, he played the leaders of both factions, the player's wingman, and ATC at the base they were due to land at, in one scene.
It's worth mentioning that Scott himself gets a real kick out of this trope, and frequently recites some of his more popular Talking To Himself scenes (particularly from Beast Wars) for audiences at anime conventions.
Peter Cullen played both Optimus Prime and his right hand man, Ironhide (meaning that he's talking to himself in the first post-credits scene of the 1986 movie). Frank Welker voiced Megatron, Soundwave and most of the first-year Decepticons aside from Starscream. This is perfectly demonstrated in this clip, in which he voices all the Decepticons.
In Animated, David Kaye is Prime, Grimlock, Lugnut, Cliffjumper, Warpath and Highbrow. Jeff Bennett is Prowl, Ultra Magnus, Captain Fanzone, Soundwave, Angry Archer, and Mixmaster. Bumper Robinson is Bumblebee, Porter C. Powell, Blackout, and does three voices for Blitzwing, whose Split Personality occasionally talk amongst themselves. Tom Kenny is Starscream (as well as all of the Starscream clones except the female one), Isaac Sumdac, Scrapper, Wasp, and Jetfire. Corey Burton is Megatron, Ratchet, Shockwave (reprised from G1), Longarm Prime (who is Shockwave but has a slightly different voice), Colossus Rhodes, Ironhide, and Spike. Besides Sari, Tara Strong is pretty much every female and child except Blackarachnia, Arcee, and a brief appearance by Flareup. Bill Fagerbakke is Bulkhead and Hot Shot. While he only voiced Jazz for the first two seasons, in the third Phil LaMarr is also Oil Slick, Jetstorm, and replaces Kevin Michael Richardson as Omega Supreme. Most of them also do a few minor characters. Come to think of it, Animated has this at least as bad as the original did.
Lampshaded in a script-reading called Bee In The City, which had Bumblebee suggest to Beast Wars Megatron (also voiced by David Kaye, who was doing Prime in the same reading) that they try to get help from Lugnut or Grimlock. Megatron responded, "Who do I look like, Scott McNeil?"
Billy West has an exceptional range, playing five recurrers on Futurama (Fry, Farnsworth, Zapp Brannigan, President Richard Nixon's head, and Zoidberg), three of whom are main characters, meaning this trope is in effect in almost every episode. He also plays both Ren and Stimpy from The Ren & Stimpy Show (after Ren's original voice actor, John Kricfalusi, was fired from Nickelodeon, though West was originally supposed to be both Ren and Stimpy) and also playing the modern versions of most of the characters Mel Blanc was known for (along with Jeff Bergman, Gregg Berger, Greg Burson, and others). Hell, Billy can do things with his voice that normally require electronic alteration to achieve (case in point: the energy being first seen in "Love Labor's Lost in Space." According to commentary, the producers shut down the recording studio after Billy said his lines, not knowing until later that it wasn't an audio problem; it was Billy West speaking that high).
Besides Billy West, there's also Tress MacNeille, who doesn't do any regulars, she does pretty much every secondary female character, most notably Linda the female reporter, Petunia, Hattie McDoogal, and Mom of Mom's Friendly Robot Company. There's also Lauren Tom, who voices both Amy and her mother.
John DiMaggio:(commentary) I love it when Billy gets to talk to himself during scenes.
One Futurama commentary laughs at the fact that a very funny scene is really just John having a bitchy argument with himself. He shrieks in delight that he's just like Billy now!
In addition to Bender, Di Maggio plays recurring characters Url, Randy, Sal, Elzar, Flexo, Joey Mousepad, Ignor, Robot Santa note except in his first appearance, where he was played by John Goodman and Fry's dad as well as various incidental characters.
Gets meta in Leela and the Genestalk when the crew find Jake and Finn trapped in Mom's floating Genetics lab. Both Bender and Jake are voiced by John Dimaggio.
Jake: What time is it? Bender: Time for you to shut up!
Maurice LaMarche is, well, Maurice LaMarche. His range is well established in Futurama with Kif Kroker and Lrrr (of the planet Omicron Persei VIII) as extremes. Though he's not above mocking a certain lack of variety in his characters on the commentary for the episode "The Route of All Evil".
David X: Tell me, can you show us the difference between Morbo, Lrrr, and the H.G.B? Maurice: This is Morbo! (virtually identical voice) This is Lrrr! (virtually identical voice) And this is the Horrible Gelatinous Blob!
His lack of variety thing can be seen in The Real Ghostbusters as well — in "Night Game", an episode wherein Winston plays a game of baseball that will decide the fate of a single human soul, Maurice provides the voice for the Umpire as well as for Egon. It's vaguely amusing, actually, since the Ump was just Egon with a large reverb!
Almost the prototype example, Mel Blanc did all the male voices in most of the Looney Tunes shorts (with some minor exceptions, like Elmer Fudd), so unless Granny or another female character was needed, Mel Blanc was the only voice actor. He did, among others, Bugs, Daffy (which was his Sylvester voice pitched up), Porky, Tweety, Yosemite Sam, Pepe le Pew, Foghorn, Marvin, The Tasmanian Devil, Wile E. Coyote (when he spoke), Elmer Fudd (after the death of Arthur Q. Bryan), and Sylvester (apparently the closest to his natural voice). The Bugs Bunny Show's theme song even features a duet between Bugs and Daffy.
And if they did need a female voice, it was usually Bea Benaderet or later, June Foray.
In the cartoon "Hollywood Steps Out" Kent Rogers voiced all of the male celebrities with the exception of Jerry Colonna (voiced by Blanc), while Sara Berner voiced all the female celebrities.
In the short lived 1999 cartoon Rayman: The Animated Series, Danny Mann voiced both Rigatoni and Lac-Mac, and Carlos Alazraqui voiced both Razorbeard and Cookie. So not only did Mann get to order himself around, Alazraqui got to argue with himself...in the same episode.
Lampshaded in one episode, in which Peter (Seth MacFarlane) tells Dr. Hartman (Seth MacFarlane) that he sounds almost exactly like his father-in-law, Carter Pewterschmidt (Seth MacFarlane). Carter randomly shows up at that moment and has a conversation with Dr. Hartman where they wonder how they hadn't noticed it before.
Also in the episode "Baby Not on Board" after realizing that they left Stewie home alone, Brian tries to do an impression of how Stewie must have reacted. He then admits that, "Well, I can't really do a good Stewie." Both characters are played by MacFarlane.
In the 1996 Cartoon Network short Larry and Steve, which Seth MacFarlane made when he was at Hanna-Barbera (and was essentially a Family Guy prototype), MacFarlane voiced all the male characters, including Larry (whose voice was identical to Peter Griffin), Steve (a dog with a voice like Brian), and a pilot who sounds like Quagmire. The only other cast member was Lori Alan, who went on to do voices for Family Guy.
It becomes a Crowning Moment Of Awesome when Quagmire delivers a well-deserved "The Reason You Suck" Speech to Brian, voicing every concern the viewers built up over the years over Brian's actions, because it can easily be imagined (or interpreted) as Seth MacFarlane being called out for his own shortcomings by one of his creations (Imagine it like Who Framed Roger Rabbit? if it was a Woody Allen-esque character study).
In the original Life of Larry (MacFarlane's student film for animation), to which Larry and Steve was a sequel, he did all the voices, including Larry's wife Lois.
American Dad! isn't as reliant on this trope, with most of the characters having their own voice actor. Nonetheless, the two most important characters, Stan and Roger, are both voiced by MacFarlane.
Also pointed out in MacFarlane's Hulu commercial and his monologue on the Saturday Night Live episode he hosted, which has him going from Brian (or his normal voice, since they're one in the same) to Peter to Stewie to Quagmire (and on his SNL monologue, it was the same thing, only Roger the alien and some celebrity impressions was added).
Seth Green also does multiple voices. Two main characters, Chris Griffin and Neil Goldman, and many walk-ons. He also does most of the voices on Robot Chicken, so he no doubt talks to himself a lot on that.
Taken to the extreme in the Family Guy episode "Brian and Stewie", in which the titular duo are the only characters to appear and they're locked in isolation, so all they can do for the half hour is play off each other. It's literally 22 minutes of Seth MacFarlane talking to himself. And then there's the "Fellas at the Freakin' FCC" musical on the episode "PTV"note The one where Peter creates his own TV network of raunchy shows after the FCC begins censoring shows like Three's Company, The Honeymooners, and The Dick Van Dyke Show because of complaints of David Hyde Pierce indecently exposing himself on live TV with MacFarlane voicing all three singers (Brian, Peter, and Stewie).
Bump In The Night has multiple scenes in which Bumpy and Destructo, both voiced by Jim Cummings, have lines. The show also contains other one-time characters with his voice.
On Aqua Teen Hunger Force, Dave Willis voices Meatwad, Carl, and Ignignokt. Most episodes feature Carl interacting with Meatwad, and any Mooninites episode will usually feature Ignignokt interacting with both of them.
Rocko's Modern Life has roughly five main characters (if you count Rocko's dog Spunky), and a lot of recurring characters, yet, the show had only five people in the main voice cast; four of them male actors, and only one actress. They consisted of Carlos Alazraqui (voices Rocko, Spunky, Leon Chameleon, Squirmy, and a few other incidental male characters), Tom Kenny (voices Heffer, Chuck Chameleon, Mr. Smitty, Peaches, Flecko, Really Really Big Man, Bloaty, the Newscaster, and practically half of the incidental male voices on the show, as well as a few incidental females), Doug Lawrence (voices Filburt, Peter Wolfe, and a few other incidental characters), Charlie Adler (voices Ed and Bev Bighead, George Wolfe, Grandpa Wolfe, Gladys the Hippo Lady, Mr. Dupette, and several other incidental males and a few females as well), and Linda Wallem (voices Dr. Hutchison, Virginia Wolfe, Cindy Wolfe, Tammy, and many other incidental female characters.) Though there were a few minor exceptions, such as Richard Simmons voicing himself in an early episode, and series creator Joe Murray voicing Ralph Bighead (and himself in one episode).
A Static Shock episode, "A League of Their Own", had Phil LaMarr voicing Green Lantern and Static. One of the creators (either Paul Dini or Bruce Timm) commented that he wanted to do more of Static and GL talking, to drive Phil nuts. They got to do so in the episode "Fallen Hero", which features only John Stewart as the guest hero of the episode.
Maria Canals-Barrera voiced both Shayera Hol and Fire. In the episode "I Am Legion", Shayera and Fire share every scene with each other.
Jennifer Hale handles Killer Frost and Giganta. In the latter's first episode, Grodd puts them through a series of trust exercises, with little Frost catching immense (6' or so) Giganta... who is letting herself fall off a cliff into Frost's arms. Predictably, pain ensues.
And in the episode "Injustice For All", Mark Hamill voiced both Joker and Solomon Grundy, who of course start arguing.
In the Batman: The Animated Series episode "Perchance to Dream", Bruce Wayne talked to his father — also Kevin Conroy. Even better: in that same episode, Bruce has an argument with his alter-ego. Conroy is said to have switched between his "Bruce Wayne" and "Batman" voices in real time, rather than recording the characters separately.
All these examples of Batman are literalised examples of the character talking to himself, so it's no real surprise...
Tim Daly, the voice of the titular character from Superman: The Animated Series, also voiced Bizarro, which is justified in that Bizarro is a clone of Superman, but they sound different as the former sounds more guttural and simple and backwards than the first. In one sequence, a yet to be corrupted Bizarro does talk as Superman and at one point saves Clark Kent from falling.
This was carried over to Justice League Unlimited, following (though with a three-year delay) the change of Superman's voice actor from Tim Daly to George Newbern, even though he and Superman don't interact directly here.
The Boondocks does this a lot because two of the main characters (Huey and Riley) have the same woman, Regina King, doing their voices.
In the episode "The Color Ruckus", Gary Anthony Williams voiced not only his regular character, Uncle Ruckus, but his brothers Darrell and Darryl as well.
Drawn Together makes extensive use of this practice by having its actors voice numerous minor characters in addition to their regular roles. Most of the female characters are voiced by Cree Summer or Tara Strong while most of the male characters are voiced by Jess Harnell or James Arnold Taylor. Strong, in fact, voices two regular characters, Princess Clara and Toot Braunstein. In one DVD commentary, the creators state that they often give Clara and Toot scenes together just to watch Tara have conversations with herself.
This show features a situation where two characters, Jérémie and Aelita, are voiced by the same actress [Sharon Mann]. Because the two characters are both best friends and the show's most blatant and canonical couple, this must've been fun to watch for everyone in the voice acting studio.
Another example from the same show is David Gasman, who has a laundry list of voiced characters: a gruffer "older guy" voice used for the likes of Jim, Mr. Ishiyama, and various minor MIB, TV reporters, and teachers, and a lighter "kid voice" used for Herb, William, Chris [Jim's nephew] and various students.
In the Mexican dub, voice actor Óscar Flores often does the voice of Nigel Uno and one of the several secondary characters that he also interprets. Still, in an episode where three of his characters appeared, he voiced only two.
In the original English-language version, Ben Diskin voices both Numbuhs 1 and 2.
Also, Lauren Tom is again her own mother, with Number 3 and Mrs. Sanban; and Cree Summer is 75% of an entire family, being Number 5, her older sister Cree, and their French-accented mother, all seen having dinner together in one episode.
And Dee Bradley Baker voices Numbuh 4 along his baby brother Joey and many villains like Mr. Fibb, The Toilenator, Lunk, and Heinrich,and many of the monsters.
Tress MacNeille played both Gadget and, yes, Chip. They talked to each other. (And spoke simultaneously in other situations, including but not limited to "Rescue Rangers away!", but that's another story.)
This video shows just how similar their voices are: the pitch (but not the speed) is increased to achieve Chip's voice.
The Spectacular Spider-Man already has a few instances of this. John DiMaggio's Hammerhead coaxes his Flint Marko into adopting the Sandman identity. Clancy Brown's Captain Stacy tries to order his Rhino to stand down. Daran Norris performs both sides of a conversation between J. Jonah Jameson and his son John. Steve Blum plays both the Green Goblin and a thug that he recruits.
Hynden Walch played both Starfire and her evil sister Blackfire — and the characters ended up fighting pretty much every time Blackfire showed up. Scott Menville also played Robin and Red X — which made sense since the first time the character showed up he really was Robin, but all of his subsequent appearances were when an unnamed villain stole the old Red X suit.
Not to mention when Beast Boy faught Adonis in "The Beast Within". Both characters were voiced by Greg Cipes.
Taken to a bit of an extreme with the episode "Hide and Seek", which has Tara Strong as Raven and baby Teether, and Russi Taylor (voice of Minnie Mouse since the mid-1980s and Martin Princenote the nerd in Bart's class first seen on "Bart the Genius," though his first major role was in season two's "Bart Gets an F" and the purple-haired twins, Sherri and Terrinote first seen on "Homer's Odyssey," but, like Martin, didn't really have a major role until "Bart Gets an F" in the scene where they purposely tell Bart the wrong answers so he'll fail his test, on The Simpsons since the 1990s) as Melvin and Timmy. The four characters spend the entire episode together, starting from before the theme song even starts. Of course, there were only a total of six main characters in the episode, but still...
On Superfriends, Shannon Farnon did most of the female voices, including Cheetah. As Seanbaby points out, if you couldn't see the screen, it "sounded like Wonder Woman was kicking her own ass."
Likewise, every female character on Thundercats except Wily Kit sounded an awful lot like Cheetara doing a Katherine Hepburn impression.
Wendy Hoopes voiced both Helen and Quinn Morgendorffer. In the Musical Episode, she even sings a duet with herself. Plus she voices Jane Lane, who also converses with each of the other two at least once.
There's also Timothy O'Neill and Anthony Demartino (Both voiced by Marc Thompson), who have a lot of conversations together.
Gets a bizarre Lampshade Hanging in the season finale of Stroker and Hoop, where it turned out all of the extras that had the same voice were actually all the same guy, who was taking revenge after the title characters ruined his life over and over again. Doubly so because Jon Glaser does the voice of both that guy and Stroker.
Grey DeLisle does this on the finale of Avatar: The Last Airbender where she as Princess Azula berates herself as a handmaiden for leaving a pit in her cherry. Though they didn't actually end up talking to each other she ended up playing Ta Min [Roku's wife] and Kya [Katara and Sokka's mother], as well as the actress-playing-Katara in the episode Ember Island Players.Dee Bradley Baker is also most of the animals on the show (and Chong), so there's all the time Momo and Appa were bickering with each other.
And twins Jeanette and Therese in Vampire: The Masquerade – Bloodlines, who can often be found arguing with one another. Very loudly. And, in fact, turn out to be a single person — Tourette — with severe split-personality disorder, meaning that she is literallytalking to herself.
With Richard Steven Horvitz doing both Billy and his father Harold (Horvitz also does Billy's grandfather in one episode), Greg Eagles doing Grim and Sperg, and of course Phil Lamarr doing Irwin's entire family (sans him and his mom, whom were also voiced by the same person, Vanessa Marshall); his father, his grandmother, and grandfather Dracula.
Note, though, that Irwin, a young black boy, is voiced by an adult white woman. ComicCon panel interviews confirm that she was unaware of Irwin's ethnicity when first introduced to the character's design as a colorless sketch. note Before people cry Unfortunate Implications, note that this is no Double Standard; the aforementioned Lamarr, who is African-American, has voiced several Caucasian and at leasttwo Asian characters.
H. Jon Benjamin does the voices of both Coach McGuirk and Jason, and converses with himself quite often.
Lampshaded in the "Home Movies Drinking Game" on the Season One DVD set: the viewers are told to yell "Jon-Jon!" whenever this happens, and whoever yells first has the power to make anyone or everyone do a shot.
All characters except guest star voices are done by the same six people. In one episode, three teenaged characters all played by H. Jon Benjamin have several lengthy scenes together.
This is subverted in an outtake that was featured on The-n.com, where a completely different actor is trying to come up with a suitable voice for a one-time character and he sounds suspiciously like one of Benjamin's regular teen characters. The teen in question then asks the other actor, "Father? What are you doing here?"
Frank Welker voiced both Baby Kermit and Baby Beaker, while Greg Berg voiced both Baby Fozzie and Baby Scooter, and in the first two seasons, Howie Mandel assumed triple duty as Baby Animal, Baby Skeeter and Baby Bunsen Honeydew. In the third season, Howie Mandel left the show, and Dave Coulier (a.k.a. Joey Gladstone of Full House) took over as Baby Animal and Baby Bunsen, while Frank Welker took over the triple-duty, voicing Baby Skeeter in addition to Kermit and Beaker.
Dave Coulier also voiced Bean Bunny, Janice, Statler and Waldorf. Russi Taylor voiced Gonzo and Robin.
Dee Bradley Baker does the voices of all the clones. The episode Rookies becomes almost the ultimate example of this trope, as the main plot features a number of rookie clones in over their heads being led by older, more experienced clones. The actor barely varies his voice from one to another. If you choose to annoy Karen Traviss and assume they're all one person, it's almost in-world Talking to Himself. Justified in this case, since all the clones are cloned from the same man and raised in the same setting.
Umbara arc would be the best example. Nothing but clones and one Jedi general for four episodes.
James Arnold Taylor voices both Plo Koon and Obi Wan. When they have conversations with each other, it veers into this trope.
Both Senator Stampingston and Mr. Selatcia are both voiced by Mark Hamill, with the former basically being a less raspy and malevolent version of the latter. They are part of the same group that doles Infodumps almost Once an Episode. This is very noticeable. In the same group, General Crozier and Cardinal Ravenwood are both voiced by Victor Brandt, which is less noticeable.
The entire Five-Man Band is voiced by two people. Toki and Murderface are both played by Tommy Blacha (who also voices Dr. Rockso and more); Nathan, Pickles, and Skwisgaar are all played by Brendon Small (who also voices Ofdensen), meaning he does the most Talking to Himself of the cast.
The entire list of recurring characters is voiced by maybe six people. Considering these are split into 2 groups that rarely interact, you're more likely to find someone following this trope than talking to anyone else.
Michael Bell voiced Chazz Finster and Drew Pickles who often had conversations with each other. In an earlier episode, he also voiced both of the criminals who kidnap Tommy after mistaking him for a millionaire's child.
Also, Kath Soucie voices twins Phil and Lil, who often argue with each other, as well as their mother, Betty Deville.
The actress for Didi and Minka (Melanie Chartoff, from the early 1980s sketch show Fridays and the early 1990s sitcom Parker Lewis Can't Lose), who thought it was amusing that she could have a mother-daughter conversation with herself.
In Beavis And Butthead, Mike Judge voices both the title characters and most of the adult male characters who interacted with them (the hippie teacher David van Dreisen, the militant gym coach Mr. Buzzcut, their neighbor Tom Anderson and Principal McVicker).
In King of the Hill, Mike Judge voices Hank Hill, Boomhauer and Stuart Dooley; Lauren Tom voices Connie Soupanoosinpone and her mother Mihn; Toby Huss voices Cotton Hill and Kahn Soupanoosinpone; Pamela Adlon voices Bobby Hill and Clark Peters, and Stephen Root voices Bill Dautrieve and Buck Strickland.
Jim Cummings (a voice actor of considerable talent) is the voice of both Winnie the Pooh and his best friend Tigger, ever since halfway through the late-1980s Saturday morning series (although Paul Winchell did return for the sequel film).
... And the voice of Darkwing Duck and his Evil Counterpart, Negaduck. Darkwing also talked to Herb Muddlefoot and Professor Moliarty, who were also... Jim Cummings!
And Bonkers and his partner, Lucky Piquel, in Bonkers
Similar to the example for Tom Kenny above, both he and fellow Handy Manny VA Nika Futterman have this happen a lot to their characters; Tom Kenny voices Pat, of the main cast and Mr. Lopart of the supporting, who occasionally have dialogues. Nika Futterman has it happen a bit more though, because both her main characters (Stretch and Squeeze) will frequently chat between themselves, and she also voices many of the adult female supporting cast members. Another VA, Carlos Alazraqui, also has this happen to a degree because besides Felipe in the main group, he also voices many of the adult male supporting cast.
In the series The Animals of Farthing Wood, Rupert Farley voiced Fox, his sons Bold and Friendly, his grandson Plucky, Mr. Hare, Mr. Peasant, Measley and Mr. Newt; Stacey Jefferson voiced Vixen, her daughters Charmer and Dreamer, Adder, Kestrel, Lady Blue and Mrs. Rabbit; Ron Moody voiced Badger, Toad, Mr. Hedgehog, Mr. Vole, Mr. Fieldmouse and The Great White Stag; Jon Glover voiced Scarface, and his sons Ranger and Bounder; Jeremy Barrett voiced Whistler, Mr. Rabbit, Mr. Shrew, Mole and his son Mossy; Sally Grace voiced Owl and Weasel, and Pamela Keevilkral voiced Whisper, Mrs. Squirrel, Mrs. Hedgehog, Dash, Cleo and others.
In Star Trek: The Animated Series, the regulars also did many of the one-shot guests (and even secondary and recurring characters). With rare exception, any woman you hear that wasn't a member of Star Trek: The Original Series' main cast will be voiced by Majel Barrett (when they're not voiced by Nichelle Nichols), and any man will be voiced by James Doohan (a.k.a. Scotty). This means there are several conversations in which the two Talk To Themselves — even if Scotty and Nurse Chapel aren't in on the conversation.
Most of the main characters are voiced by either Phil Vischer or Mike Nawraki, the series' creators. A recurring trick is that whenever there is a pair of closely-associated characters (Jimmy and Jerry Gourd, the French Peas), one is voiced by Phil and the other by Mike, but the voices are performed similarly.
Over the years some of the minor characters have started sounding more like the major characters voiced by the same actors. This is finally lampshaded when Larry comments that he had always thought Archibald was the announcer for the "Silly Songs with Larry".
An episode has the Mayor and the Narrator (both voiced by Tom Kenny) talking to each other.
Other examples in the show include Brick and Boomer of the Rowdyruff Boys are voiced by Rob Paulsen, the Gangreen Gang is voiced by two people (Jeff Bennett voices Ace, Big Billy, and Grubber and Tom Kenny voices Snake and Arturo), and all three members of the Amoeba Boys are voiced by Chuck McCann.
The episode Sweet n' Sour features a trio of cuddly talking animals committing robberies. The animals are voiced by the same actresses as the Powerpuff Girls.
X-Men: Evolution episode "Ascension", Professor X and Apocalypse were arguing with words, both voiced by David Kaye.
Bernard Cribbins provided the voices of all the main characters on the original The Wombles.
The first one had a handful of actors performing multiple roles, so you'd have Cam Clarke doing both Leonardo and Rocksteady, Barry Gordon as Donatello and Bebop, Pat Fraley as both Krang and Baxter Stockman, and Tress MacNeille as two of the three Neutrinos.
Although rarer in the second cartoon, since characters voiced by the same actors tended not to appear together, it also had a handful of examples, mostly involving voice actor Sean Schemmel, the most notable being with the Foot Mystics, a five-man mini-boss squad voiced entirely by Schemmel and fellow actor Brian Maillard.
In the Mexican dub of the first cartoon, both Shredder and Krang were voiced by voice actor Herman López.
The season 4 episode "The Revenge Society" has Urbaniak in a three-way conversation with himself.
The season 3 episode "Shadowman 9: In the Cradle of Destiny", an episode with over a dozen characters, was voiced entirely by three people.
In Jungle Cubs, Jason Marsden in the first two seasons voiced both Shere Khan and Louie who often had arguments.
The Mexican dub of Dennis the Menace had voice actress Patricia Acevedo do the voices for Joey, Margaret and Alice [Dennis' mom]. Likewise, Dennis and Gina are both voiced by voice actress Gabriela Willert.
Likewise in the English version, Phil Hartman and later Maurice LaMarche voiced Henry Mitchell, Mr. Wilson and Ruff, Marilyn Lightstone voiced Alice Mitchell and Mrs. Wilson, and Jeannie Elias voiced Joey, Margaret, Tommy and P.B.
A crossover episode of The Mask had the main character interact with Ace Ventura. The Mexican dub had both characters being voiced by Mario Castañeda.
Cartoon Network's relatively new Marvel project, The Super Hero Squad Show, has Tom Kenny as regulars Iron Man, MODOK, and Captain America, all of whom almost always end up interacting in one combination or another. They also have Steve Blum as both Wolverine and Abomination, who again, get a lot of screen time together (and in one episode actually play a round of golf).
The only Omnitrix aliens in Ben 10: Alien Force and Ben 10: Ultimate Alien who are not voiced by Dee Bradley Baker are Alien X, Ghostfreak and Rath; even then, the latter two have voices outside of the aliens (Azmuth and Will Harangue, respectively and for starters). But since the aliens hardly interact with one another (being part of the same person and all), it's mostly averted.
Yuri Lowenthal voices Ben and Albedo. Justified in that the latter was stuck in Ben's human form (long story).
We also have Ashley Johnson, who, in one episode, provides the voice for main character Gwen and her distant cousin, Sunny.
In fact, this was intentionally avoided in the episode "Fused": by having Lowenthal as the voice of Omnitrix alien AmpFibian in his first appearance because Baker was already Ra'ad (the alien who supplied the DNA but was temporarily still a part of Ben). In future episodes, Baker had replaced Yuri as the voice of AmpFibian.
Due to the limited amount of main characters of KaBlam!'s Henry and June shorts, many of the one-appearance characters will be done by a member of the regular cast (most notably is Billy West, who did most of the recurring characters). One of the most shown examples was in "A Nut in Every Bite!", in which Dawn, the executive's grand-daughter comes to visit the show. Dawn was done by Julia Mcilvaine, who did June, one of the main characters.
From 1999 to 2001, Scott Innes voiced both Scooby-Doo and Shaggy Rogers. You only have to watch half an episode to understand how often those two interact.
Jaleel White voices all three of the characters in Sonic Underground (Sonic, Manic, and Sonia), which takes talking to himself to a whole new level.
Fanboy and Chum Chum has him voicing a good 60% of the cast, and there are three straight cases of Talking to Himself - in "Sigmund the Sorcerer", where Sigmund and the Necronomicon have a conversation, in "A Bopwork Orange" where Boog and Agent Johnson talk to each other several times, and on a few occasions when Man-Arctica and his Arch-Enemy, The Global Warmer are interacting.
On Jimmy Two-Shoes, Sean Cullen voices both Lucius VII and his father, Lucius VI.
Happens with many characters on The Mr. Men Show. Perhaps the strangest example is Mr. Grumpy and Mr. Happy in the US dub.
Frank Welker also voices both Odie (reprising the role from Garfield and Friends) and Garfield on The Garfield Show. Welker also voices various extras and secondary characters. In one episode, Garfield is terrorized in a nightmare by a talking scale (also voiced by Welker); over the course of the dream, the scale slowly changes its shrill voice until it winds up with Welker's Dr. Claw voice. Jason Marsden also does several voices on the show.
Rainbow Dash and Applejack are both voiced by Ashleigh Ball. Carried to extremes in "Fall Weather Friends", where both ponies spend the entire episode arguing with each other.
Fluttershy and Pinkie Pie are voiced by Andrea Libman.
Rarity's voice actor, Tabitha St. Germain, also voices Princess Luna/Nightmare Moon, Granny Smith, Mrs. Cake, Rarity's mom, and Photo Finish. The only time Tabitha actually talks to herself is in the episode with Photo Finish, "Green Isn't Your Color." and "Sisterhooves Social", in which Rarity talks to her mom. Tabitha also voices some of the background ponies, including fan-favorite Derpy Hooves.
Tabitha St. Germain had a lot more of this in the Generation 3 My Little Pony cartoons where she played Minty, Wysteria, and Thistle Whistle, though it was less of an issue for one-shot character Fiesta Flair and the Core 7's Scootaloo.
She also voices Twilight Sparkle in the recordings done at The Ocean Group (Tara Strong, Twilight's voice actress, is based in Los Angeles, The Ocean Group is in Vancouver), so while she does a lot of this (for example, most of season 2 episode 4 is Twilight talking to Luna, not to mention all the times Rarity and Twilight have a conversation), most of it is dubbed over later.
In an in-universe example, in "Party Of One" Pinkie Pie goes a little crazy when she believes her friends don't attend her parties anymore. So she makes new friends... out of a pile of rocks, a dust bunny, a bucket of turnips and a sack of flour. And then starts arguing with them. They argue back (she's voicing them, of course.)
Michelle Creber provides both the voice for Apple Bloom and the singing voice for Sweetie Belle (another actress provides Sweetie Belle's speaking voice). This falls into this trope due to songs like "Perfect Stallion", in which both Apple Bloom & Sweetie Belle sing.
Averted as of Season 4, where Claire Corlett has taken over Sweetie Belle's singing voice.
Britt Mc Killip, the voice of Cadance, and Queen Chrysalis when she is impersonating Cadance in "A Canterlot Wedding", also voiced Lyra Heartstrings, who is one of the brainwashed bridesmaids.
On The Penguins of Madagascar, James Patrick Stuart voices both Private and Joey, and John DiMaggio voices both Rico and Burt. The former is interesting in that Stuart is a California native, but he uses a British accent for the former and an Aussie accent for the latter. The two characters also have a conversation in "Kanga Management".
In Regular Show, J.G. Quintel voices Mordecai and High-Five Ghost, and Sam Marin voices Benson, Pops and Muscle Man. In his first appearance, High-Five was voiced by Jeff Bennett, who splits most of the background character voices with Mark Hamill (Skips). William Salyers as Rigby is the only VA who doesn't pull double duty. Roger Craig Smith provided voices for many of the show's antagonists before landing a recurring role as Thomas.
Tatasciore also does some taking to himself in an episode guest-starring the Fantastic Four, as rivals The Hulk and The Thing.
Another character Fred Tatasciore voiced, Volstagg the Voluminous, became one of the first mythological beings to greet the Hulk to his realm.
Rick D. Wasserman voices The Mighty Thor and the Absorbing Man, who have a fight in "Gamma World" while exchanging battle cries.
Robin Atkin Downes voices Baron Zemo and The Abomination, the two Masters of Evil who argue the most.
Danger Mouse had David Jason as Danger Mouse, Flying Officer Buggles and Count Duckula. (Edward Kesley was Colonel K and Baron Greenback, but the format of the show meant they didn't interact.)
The Adventures of Blinky Bill takes this trope to the extreme, with only 2 voice actors in the whole series: Keith Scott and Robyn Moore.
Rocky and Bullwinkle ran into this quite a bit, since the entire show only had about five voice actors working on the whole show. Whenever a male side-character talked, it was either Bill Scott (Bullwinkle, Fearless Leader, Gidney) or Paul Frees (Boris, Captain Peachfuzz, Cloyd), and whenever a female character talked, it was ALWAYS June Foray, who voiced Rocky and Natasha. This includes the supporting shorts too (which Daws Butler was often a part of). As you can imagine, the voice actors were having a LOT of conversations with themselves.
As the years pass and the old voice actors pass away, this trope is in effect more and more—Keith Scott, animation superfan, has taken over for Bill Scott, Paul Frees, and narrator William Conrad.
Most of the characters in Taz-Mania were voiced by only a handful of people, though only a few instances involved interaction between characters with the same VA (given how Taz himself was generally the central character of nearly any given episode). Taz himself was voiced by Jim Cummings, who also voiced Bushwhacker Bob (Taz's boss), Wendal T. Wolf (a minor character who would bother Taz in attempting to befriend him) and Buddy Boar (Taz's self-appointed best friend). In addition, both Taz's father and uncle (Hugh and Drew) were voiced by Maurice LaMarche, who, in the episodes that Drew featured in, interacted almost exclusively with one another.
King Leonardo And His Short Subjects: Jackson Beck was King Leonardo and Biggy Rat; Allen Swift was Odie Cologne, Itchy Brother, the narrator, and the King's twin nephews Duke and Earl.
The Beatles cartoon: Paul Frees was John and George, Lance Percival was Paul and Ringo.
In all the old school Donald Duck cartoons not only was Donald voiced by Clarence Nash but so were his nephews Huey, Dewey, and Louie; so every short that exclusively focused on the four of them was simply just Mr. Nash providing all the voices. Not only that, but in her first few appearances Nash voiced Daisy Duck as well. The short "Mr. Duck Steps Out" solely features Donald, Daisy, and the nephews, with Nash voicing all five.
For that matter, with the exception of Quack Pack which gave them each a distinct voice, this trope always counts for the nephews. All three are always voiced by one singular actress or actor.
And speaking of Huey, Dewey, and Louie appearances, we might as well add in DuckTales as well. Russi Taylor voiced not only the nephews but also Webby, and the four often worked together being the main kids on the show. The four main Beagle Boys (Big Time, Bouncer, Burger, and Baggy) were voiced by two actors each: Frank Welker as Big Time and Baggy, and Chuck McCann as Bouncer and Burger. Hal Smith also provided the voices of Flinthart Glomgold and Gyro Gearloose, and although not as common as the previous two examples, the two characters did share a couple scenes together; for example one early episode has Glomgold hire Gyro to build giant construction robots for him.
Chris McCulloch (aka Jackson Publick) voices Paul (the more flamboyant of the two gay inmates), Ash, Nicky, and a good deal of other inmates that often communicate with each other.
Richard Mather voices the Twins, their older triplet brothers, and their father. All of these characters managed to interact in "Troubles with Triplets".
Sally Donovan initially had just the roles of the Mistress and Nova to play, but has since taken on the roles of Charise and the Ultraprison inmates. If there's a female bit character, chances are that it'll be her providing the voice.
Kamala Sankaram originally provided the voices of Charise and the lady inmates, with all characters managing to share a sequence of dialogue together.
On Gravity Falls, series creator Alex Hirsch voices both Grunkle Stan and Soos. He has also voiced Old Man McGucket, Quentin Trembley, and a few incidental characters.
The Littles: Ken Sansom voiced both Dr. Hunter and his assistant Peterson.
Samuel Vincent seems to be the go-to guy for male one-shot characters in Littlest Pet Shop (2012), regardless of if he's human or pet. While this doesn't create dialogue with himself most of the time when he plays a human (though Josh, an important minor character, is voiced by him), Vincent voices Russell, the pet with the most lines and the second-most screentime. Hence, when Vincent voices a pet, he will have to hold both sides of a conversation when Russell inevitably speaks to him, as is the case of Esteban and Old Bananas.