1977's Yatterman by Tatsunoko Production had the Dorombo gang consisting of Doronjo (Noriko Ohara), Boyacky (Jouji Yanami) and Tonzura (Kazuya Tatekabe). Following Yatterman is Zenderman, Rescueman, Yattodetaman, Ippatsuman, and Itadakiman, and they all featured expies of the first trio all voiced by the same trio of seiyuu. So you can imagine what happens when all of these trios would meet in the 1993 Time Bokan OVA....
There is frequent doubling among the actresses playing the 31 schoolgirls from Negi's class in the North American dub of Mahou Sensei Negima! It's relatively common to find two or more girls all performed by the same actress chattering among themselves:
Alison Retzloff plays both of the twins Fumika and Fuuka Narutaki, who are always talking to each other.
Monica Rial plays Konoka Konoe, Kazumi Asakura and Satsuki Yotsuba; in episode 16 she has to voice both sides of a "sports announcer" team when Konoka and Kazumi host a contest broadcast to the dorm TV set.
Notably averted in the original, where each girl has a different VA, quite impressive.
Shaman King's dub also had this with the main hero Yoh Asakura and the Big BadHao being voiced by the same actor, Sebastian Arcelus, which made the later interactions and fight scenes all the more impressive.
Chiwa Saito voiced lead Action Girl Subaru, her antagonist counterpart Nove, andThe Dragon, Quattro. Particularly impressive considering that one is a Genki Girl, one is angry all the time, and one is dripping villainy.
Kaori Mizuhashi did Yuuno, Vivio, and Sein, though this is generously averted in the TV series as Yuuno was Demoted to Extra. Yuuno and Vivio talked to each other in Vivid, but it is a comic series. However in the PSP game The Gears of Destiny, Yuuno and Vivio played this straight. In a likely reference to this piece of trivia, Yuuno is the first person Vivio fights against when she appears in the game.
Mai Nakahara did Teana, Laguna Granscenic and Megane Alpine, also averted.
Marina Inoue did Cinque, Wendi and Erio, so this is played straight.
Eriko Kigawa did Ginga, Uno and Tre. In StrikerS Sound Stage X, all three characters share the same dialogue. One is a nice young women, the other is more or less evil adult woman with a matured voice, the other one is a androgyne woman with an even deeper and angry voice. The latter two are not amused to talk with the former.
Christopher Sabat is most notable in the English version, playing Vegeta, Piccolo, Yamcha, Shenron, Zarbon, Jeice, Burter, Recoome, Guru, Moori, Kami, Mr. Popo, Turtle, Colonel Silver, Grandpa Gohan, Korin, Borgos, Officer Black, Omega Shenron, and countless others. This led to a hilarious slip-up when Vegeta's line of "Now what?" in internal monologue came out in Jeice's voice instead (it was subsequently corrected for the remastered release).
Stephanie Nadolny voiced all of the male members of Goku's family as kids, with the exception of Goten, who was voiced by Videl's voice actress, Kara Edwards. Mike McFarland played a few characters himself, voicing Master Roshi, Yajirobe, Mez, Baby Vegeta, and others. Another frequently used voice actor was Kyle Hebert, who voiced Adult Gohan, Pikon, East Kai, the King, Appule, General White, the Ox-King, and also narrated DBZ. Dale D. Kelly voiced Ginyu and narrated a few seasons of the pre-remastered version (and used pretty much the same voice, it was obvious). In addition, Justin Cook voiced Raditz, Super Buu, and adult Dende; Linda Young voiced Frieza, Fortune Teller Baba, and Fasha; Meredith McCoy voiced Android 18, Launch, and Maron; Sonny Strait voiced Krillin, Giru, and Bardock; Brad Jackson voiced Oolong and King Cold; Monika Antonelli voiced Puar and Chiaotzu; Chuck Huber voiced Emperor Pilaf, Garlic Jr, Android 17, Mr. Robot, Mr. Shu, and Kibito; Laura Bailey voiced Dende, Kid Trunks, Hasky, Kid Chichi, Princess Oto, Ranfan, Akane, Erasa, and some appearances of young Vegeta; Susan Huber voiced Suno, Upa, young Pan, and adult Videl; Josh Martin voiced Commander Red, Fat Buu, and Kidd Buu (who spend about four episodes fighting each other); and last but not least, Sean Schemmel, the voice of Goku, also voiced as King Kai and Nail (which led to confusion sometimes). The studio's voicepool was fairly small in the beginning, mix that with the show's large cast, and you've got a lot of this!
While some of this has been corrected over time, DBZ Kai had Colleen Clinkenbeard voice both Gohan and Android 18, characters originally voiced by different actors in DBZ (Stephanie Nadolny and Meredith McCoy respectively).
It's even worse when you account for additional characters, since the voices above were recycled for those too.
The Japanese version, meanwhile, has Hiromi Tsuru (mother/daughter Bulma/Bra), Daisuke Gōri (Mr. Satan/Gyuumaou, Gohan and Goku's fathers-in-law), Yuko Minaguchi (mother/daugher Videl/Pan) and Masako Nozawa (Goku/Gohan/Goten/Bardock/Goku Jr., father/son/son/grandfather/great-great-grandson! In other words, Every male member of his family except Raditz)
Same with Kozo Shioya in the Japanese version, who voices all of Boo's forms—so in addition to the above, there's also Fat Boo and Skinny Evil Boo's brief fight.
In the Mexican dub of Dragon Ball Jesús Barrero does the voices for both Yamcha and Puar, who are always together. He only voiced them in the first 60 episodes, though.
Another example in the Mexican dub is Laura Torres, which voices Goku, Gohan AND Goten as children. They got different male VA's for their adult selves, though. Though this may not count, since kid Goku, kid Goten and kid Gohan do not interact with one another. (Except in the video games.)
In the same deal, we have Mario Castańeda, who did the voice for Adult Goku, but he also did the voice for Turles in the 3rd movie, and Bardock. He also did other voices, like the main title announcer in Dragon Ball's opening, Colonel Silver, Pamput, and the young Master Roshi in a filler. Adult Goku obviously talked with Turles in the 3rd movie, and he had a mind conversation with Bardock in a filler scene during the battle against Freeza.
This is actually a plot point in Excel♥Saga: The Great Will of the Macrocosm is, in reality, just another facet of Pedro's Wife simply on the grounds that they share the same voice actress. Lampshaded with a quick title card mentioning: "Tough; she still only gets one paycheck."
Mashiro Kazahana and Fumi Himeno share a voice actress in the original Japanese version of Mai-HiME, which partially underlines the otherworldliness of both characters.
In one scene of Gundam SEED Destiny, the two idols, Lacus Clyne and Meer Campbell face off in the ruins, resulting in their voice actress (both Japanese and English dubs — Rie Tanaka and Chantal Strand, respectively) acting out this trope.
This trope appears in an episode of Zettai Karen Children. With Rie Kugimiya playing the teleporter Mio and the psychic squirrel Momotaro, she gets a few chances to talk to herself and once, Momotaro becomes Mio's Head Pet.
Averted by the dub. In Shino Aburame's first appearance, he was voiced by Sam Riegel, who also voiced Zaku. Later on, they fight each other in the chunin exam, but by that point, Derek Stephen Prince had replaced Sam Riegel as the voice of Shino.
Something similar happened with Itachi, who was voiced by Might Guy's VA Skip Stellrecht in his brief first appearance, but Crispin Freeman had taken the role by the time that they ended up talking to each other about fifty episodes later.
They also invert is: Zetsu has a Split Personality, with two different halves of his body sounding different. In the original is was just one voice, but the ViZ dub gave each side a different voice one, so instead of one voice actor pretending to be two different characters at once, you have two voice actors pretending to be one character (though this was only in his first appearance).
There's also Gamakichi and Gamatatsu in the English version, who talk to each other in several scenes. They're voiced by Kakashi's VA, Dave Wittenberg, but don't ever talk to him.
Averted with Tobi and Madara. Originally, they were both voiced by the same actor (Naoya Uchida) but once Tobi's true identity is revealed, he is eventually voiced by Wataru Takagi the voice when Tobi was goofy, albeit with a much more serious and deeper voice. At the time when Tobi was still imitating Madara, both have never met each other again until Tobi's identity was revealed.
The English dub of Code Geass used Michelle Ruff for several voices, including Euphemia li Britannia and the stray cat that would come to be known as Arthur, who had a conversation of sorts in episode five, when they both had their first speaking roles.
Ruff also does a large portion of the incidental female characters in Zatch Bell!.
Barely averted in Lucky Star, in which she voices both Tsukasa and Minami. However, Minami is in Yutaka's group, and she's also The Quiet One.
In the 4Kids dub, there were a few examples of this, and all of them were main characters. Veronica Taylor — Ash, May, and Delia Ketchum ("The Right Place At The Right Mime" had May and Delia sounding very similar). Rachael Lillis — Misty and Jessie (and Pikachu in the first episode). Eric Stuart — Brock and James. Oh yeah, Ted Lewis did James for the first several episodes, didn't he? Well, he went on to do Giovanni and Tracey, though that's not an example.
PUSA isn't innocent of this either. Jimmy Zoppi/Billy Beach, as well as still doing Gary, took over as James and Meowth, while Michelle Knotz voiced Jessie, May and Misty.
And in both dubs, it's incredibly common for members of the main cast to also voice many of the Pokémon on the show, and in the case of Pokémon on their own teams, it essentially mean they are commanding themselves. Just look up who voices who; you'll find plenty of trainer/Pokémon crossovers.
This happens in the original Japanese, too. Megumi Hayashibara, for example, not only voices Musashi (Jessie) but also Fushigidane (Bulbasaur), Pidgeon (Pidgeotto), and Hikozaru (Chimchar).
Quite a bit less known than her main role in the series, but Ikue Otani voices Manene (Mime Jr.).
Emily Jenness voiced both Cynthia and Dawn.
Ritchie in the Indigo League ended up battling a trainer with the same voice actor.
In the current dub, Bill Rogers is the voice of Brock, Brock's Sudowoodo and Brock's Croagunk. (His Happiny is voiced by Emily Jenness.)
The Danish dub of the two first seasons initially only had two female voice actresses.. Misty had her own voice actress (Lulu Jacobsen), but Ann Hjort voiced every single other female character (Delia, Joy, Jenny, Jessie, Misty's sisters, all characters of the week etc.), leading to quite some gratuitous Talking To Herself. Later, a new voice actress was hired for some of the characters of the week, but the regulars were all still voiced by Ann Hjort. On the other hand, the dub almost averted it for the regular male characters: Ash, Brock, James, Meowth, Oak, Gary and the narrator all had different voice actors, though Meowth's actor (Peter Zhelder) also voiced Giovanni, and the male characters of the day usually shared voices with one of the aforementioned main characters.
The American dub of Seven of Seven avoids this (it prefers Hey, It's That Voice! instead), if you consider the various Nanas to be one character; if not, you have Veronica Taylor doing seven different characters (and two of them use her "Ash" and "May" voices!). The original Japanese version used seven different actresses for the seven Nanas. We later find out that it's actually EIGHT different characters
In Digimon Tamers, Renamon (and evolutions), Ruki's mother, and Ruki's grandmother are all voiced by Imai Yuka. She probably had a lot of fun when said characters had lunch together in one scene.
Digimon Adventure 02 also had Iori and Armadimon, who were partners and both voiced by Megumi Urawa in the Japanese version, and the dub had Veemon and Ken both voiced by Derek Stephen Prince. Also in the Japanese, Ken and his brother Osamu were both voiced by Romi Park.
In the Latin-American dub, Roberto Mendiola voiced Yukio Oikawa, Mummymon... and Malo Myotismon. And made the three sound very different.
Funny enough, that's exactly the case in the original Japanese as well, where Oikawa, Mummymon and BelialVamdemon are all voiced by Toshiyuki Morikawa. You really have to listen carefully to hear any resemblance between the three characters' voices.
Speaking of the Latin-American dub, Digimon Adventure's main voice cast was the same size as the group of Digidestined, which meant each main character shared a voice with a Digimon partner: Tai with Gomamon, Matt with Agumon, Sora with Gabumon, T.K. with Biyomon, Mimi with Patamon, Izzy with Palmon, and Joe with Tentomon. When Kari joined, she and Gatomon would share their voice actor with almost no differentiation, making their case the most blatant one (not to mention that, being partners, they played this trope much more frequently than the others). 02, however, recast Kari, Gatomon, and all human males besides Joe, drastically decreasing their use of this trope.
In Digimon Adventure, Jou and his older brother, Shin, are both voiced by Masami Kikuchi. In Digimon Adventure 02, Kikuchi also voiced their middle brother, Shuu, and in the CD dramas, he also voiced both their parents. In one family dinner with Gomamon, a six-person conversation is voiced by two actors. It's interesting because the characters (Jou and Shuu especially) have similar inflections, but distinct voices.
Steve Blum barely avoided it in Adventure 02 (neither Flamedramon or Raidramon got to chat up BlackWarGreymon, though Poromon gets awfully close in episode 33), but in Tamers he voices three main characters that sound completely different: Guilmon, Kenta, and Yamaki!
And then in Digimon Tamers, Steve Blum voiced 3 characters: Guilmon, Kenta, and Mr. Yamaki. There were some instances where Guilmon and Kenta were talking to each other. I quote "Kenta: Guilmon, why won't I become your partner? Guilmon: But Kenta, Takato is my tamer. Haven't you been paying attention?"
Then there's the fact that Miki and Megumi are both voiced by Karina Altamirano.
In the European Portuguese dub of Digimon Adventure 02, the six main Digidestined (Davis, Yolei, Cody, Kari, T.K. and Ken)'s voice actors ALSO voice their respective Digimon. But sadly, the voices are EXACTLY the same, save for having a slightly higher pitch. Seriously, they didn't even try. Which means that every scene in which a Digimon talks to their partner was made quite awkward.
Both the title character of Afro Samurai and his annoying sidekick/hanger-on Ninja-Ninja are voiced by Samuel L. Jackson. Turns out it's like this in series to some degree, as Ninja is a figment of Afro's imagination.
Saya's adopted little brother, Riku, and the Big Bad, her twin sister, Diva, are both voiced by Akiko Yajima in the original. So she not only talks to herself, she rapes and kills herself. Of course, poor little Riku doesn't actually do much talking during that particular interaction as opposed to whimpers of absolute terror. It also makes Diva's later transformation into Riku's appearance and using his voice all the more flawless and disturbing.
Talking to Himself is relatively rare in Brazilian dubs, especially nowadays, since there are rules about it, but there were some exceptions. In InuYasha's dub, voice actress Leticia Quinto voices both Kagome and Kikyo. In Yu-Gi-Oh!, Marik and Odion were both voiced by voice actor Jose Parisi Jr... A season later they must've noticed that the move was not wise, as Marik's voice actor was changed.
Briareos and Tereus share the same voice actor in Appleseed Ex Machina, by the virtue of having nearly identical genetic makeup.
Raivis/Latvia is a VERY weird case. In the CD dramas he was voiced by the female Rie Kugimiya, who voices the Token Mini-Moe Liechtenstein. In the anime, he's voiced by the male Kazutada (later "Kokoro") Tanaka, who also voices Poland.
While Namikawa voiced the younger South Italy for a line in the first episode, both him and Chibitalia are now voiced by the same actress, Aki Kanada. While Chibitalia's voice is shrill and the epitome of Tastes Like Diabetes, Chibiromano's voice is rougher and more fitting of his brattier, grumpier personality.
Yuki Kaida voices both China and Taiwan in the drama CDs. She's also the narrator in the anime.
Shugo Chara! has lead heroine Amu and Dia, one of her Charas, voiced by Kanae Itou. Dia is essentially a part of Amu herself, but Amu's other charas have different voices.
Sara Werec of Soukou No Strain and Mariette, the bully who torments her, are voiced by Kawasumi Ayako in Japanese and Caitlin Glass in English. Tanaka Rie also played two characters, but they never spoke to one another.
Not to mention Sherry Lynn was also Kiyone's original voice actress before Wendee Lee took over the role in later media.
In both English and Japanese, Nobuyuki and Katsuhito Masaki (Tenchi's Father and Grandfather respectively) were voiced (in Japanese) by Takeshi Aono and (in English) by Jay Hopper and later Bob Papenbrook.
Also in the English version, Matt K. Miller voiced both Tenchi and (originally) Yosho.
Jennifer Darling, who usually voiced Ayeka, was also Lady Tokimi's original voice actress. She also voiced Tenchi's aunt.
In the English dub of Pretty Sammy, Ramiya and Rumiya were both voiced by Susan Marie Brecht, while in Episode 1, Ellen Gerstell (Mihoshi's then-voice actress) doubled as Sasami's mother before Rebecca Forstadt took over both roles in Episodes 2 and 3.
Funaho and Misaki were both voiced by Grace Zandarski in OVA 2, who later voiced Achika in Movie 1.
In OVA 3, Mona Marshall voiced both Ryoko and Rea, and used pretty much the same voice.
The Swedish dub of Cyborg 009 is ridiculously blatant about this. How bad is it, then? One person does all the voice for all characters. Men, women, children, what-have-you. Any scene where any two or more characters are talking thus falls under this trope.
Occurs in One Piece when Jimbei and Moria, both voiced by Katsuhisa Hoki, briefly clash during the Marineford arc. Thankfully, the two have completely distinct voices, Jimbei's being deep and gruff while Moria's is high and shrill.
The original French dub of One Piece had this with Zoro and Sanji, who not only argue constantly, but were played with the exact same (painful) voice. Thankfully averted by the later dub.
The Funimation dub deliberately takes steps to avoid this. In the DVD Commentary, it's been stated that the V As who play members of the Straw Hat crew are typically not allowed to voice other One Piece characters (Colleen Clinkenbeard has voiced some small female roles like Moodie and Myrue, but since her main role is Luffy, it is less of an issue) so that they don't have to concern themselves with accidentally sounding like another character they happen to voice. It makes more sense when you remember that Funimation picked up One Piece when it already had 300+ episodes.
It happens though, but it's rare for a voice actor to have more than two significant roles. Cynthia Cranz has probably voiced the most though: Onion, Bellemere, Ms. Father's Day, Young Zoro (originally), and Ririka. She also once mentioned that she was the original choice to play Ms. MerryChristmas. Brina Palencia is also the main voice for Young Zoro as well as Carmen in addition to her role as Chopper.
The 4Kids dub was pretty bad about this. David Wills voiced both Buggy and Arlong, J David Brimmer voiced Captain Morgan, Gaimon, Lucky Roux, Gold D. Roger, and Crocodile. Tara Sands also voiced Miss Kaya, Nojiko, Makino, and Young Luffy, and Erica Schroeder herself voiced both Luffy and Miss New Year's Eve (Miss Double Finger).
Sailor Moon had a couple of shared seiyuu (Keiko Han as both Luna and Queen Beryl, Chiyoko Kawashima as Haruna-sensei, Shingo and Sailor Pluto), but usually the characters were too different, not allowing even for a small conversation between them. Then came the fifth season and brought in Chibi-Chibi, voiced by Usagi's seiyuu Kotono Mitsuishi — it's rather easy to pull off this trope when one of the characters has a trait of Pokémon Speak.
Worth noting that the last pair actually ends up playing the role of a Red Herring, especially with all the guesses and jokes about Chibi-Chibi being Usagi's second daughter. Had the anime followed the manga closely, the shared voice would've had a justification, as Chibi-Chibi is Sailor Cosmos, who is hinted to be a form of Usagi from a distant future. In the anime, she is a completely different entity, namely, Galaxia's own Star Seed — meaning that in this continuity she has nothing to do with Usagi apart from wanting to encourage her to defeat Galaxia.
The original DiC/Cloverway English dub has some of this, although since it had a fairly large talent pool to work with, it's not nearly as bad as other dubs. It's been mentioned that the voice directors were trying to avoid using the same voices too much. When it did happen, the most glaring example is Emilie-Claire Barlow filling in for Katie Griffin as Sailor Mars for the last 17 episodes of R before also taking over Sailor Venus for S and SuperS (when Griffin returned to voice Mars), but since she never voiced the characters at the same time, this wasn't a big deal. Another noticeable example was Barbara Radecki voicing Serena's Mother before also voicing Sailor Neptune; she also voiced Queen Serenity for one brief appearance, as well as a few monsters of the day. These were usually voiced by Maria Vacratsis early on, but were later voiced by other people like Mary Long (who also voiced Molly, and became the second voice for Katzy), Loretta Jaffelice (Diana's voice), and Catherine Disher (who also voiced Mimette). Jill Frappier, Luna's voice, was also heard as Sailor Pluto's voice for her VERY first vocal appearance in the Luna-P, and filled in as Queen Beryl during a flashback. Tracey Moore, Sailor Moon's original voice actress, later voiced one of the Doom-and-Gloom Girls, but since the voice was completely different, it was hardly noticeable. Sabrina Grdevich also voiced both Ann and Sailor Pluto, and Vince Corazza voiced Alan before he took over Tuxedo Mask. In S, Susan Aceron voiced both Sailor Pluto and Mistress 9, and Jen Gould, Hotaru/Sailor Saturn's voice, voiced Para-Para in Super S.
The Viz Media/Studiopolis dub is already invoking this trope with many voice actors voicing lead characters and smaller ones, especially monsters and characters-of-the-day. There's a very straight example in Episode 8 where Kate Higgins voices both Ami/Sailor Mercury and Garoben (the monster-of-the-day), who do briefly talk to each other.
Fairy Tail has a lot of characters played by the same person in the Japanese version. For example: Jet, Macao, Horologium, and Sagittarius are voiced by Masaki Kawanabe.
In a literal example of people talking to themselves, a bunch of characters get to meet their Edolas counterparts, leading to plenty of this trope throughout the arc.
Special mention goes to episode 98, which features Cana and Aquarius bickering with one another—both voiced by Eri Kitamura. Lucy even lampshades how similar the two are (note while Lucy makes such a statement in the manga, it's arguably more effective in the anime to compare just how similar the two sound together).
All of the five characters from Mori No Ando are voiced by Takishi Taniguchi.
To make things clearer, Conan's voice actress is voicing both Conan and a fictional version of herself. The gag was repeated when the episode was dubbed in English (Alison Viktorin, Conan's English actress, voiced the singer in the dub as well), but the in-joke about Conan teaming up with the in-universe version of his real life voice actress was lost due to the Americanization of the show that changes all the characters' names.
Several other dubs made it too. The Spanish dub played it completely straight since Diana Torres, Conan's voice actress, is a singer too.
Spanish group Luk Internacional is infamous for this, having only a few voice actors, yet doing many series with Loads and Loads of Characters. An example of this was the same VA, with the exact same voice, doing Crayon Shin Chan's Masao and Shinko-chan, among other minor characters. Amusingly, half of the Kochi Kame male characters seem to be voiced by Shin-chan's dad, recognizable because he always sounds the same.
And this doesn't just happen in anime. The same group voiced X-Men Evolution, and in Shin-chan's dad, in addition to voicing loads of secondary characters, played... Wolverine.
The English dub of Let's Go Quintuplets features Chantal Strand voicing best friends, Vanessa and Bridget. Due to their friendship, this tends to happen.
In Battle of the Planets, six VAs had the bulk of the voice work. Keye Luke, as both Zoltar (the Spectran leader) and his superior, the Luminous One, did this regularly.
A later adaptation of Gatchaman, G Force Guardians Of Space had Barbara Goodson voicing two of the team members, Aggie and Peewee. The roles in this version were also split among a small bunch of actors, due to the low budget.
In one episode of Busou Shinki, Kana Asumi voices seven characters. Justified in that all of them are Arnval model Shinki, and confusion between two of them is a plot point.