DreamWorks Animation was rather infamous for this during the mid-2000s. After Mike Myers and Eddie Murphy garnered critical acclaim for their voice acting in Shrek, Dreamworks tried to capitalize on this success with all their future movies. This resulted in the celebrity voice actors getting Billed Above the Title. Teasers of their future films would often consist of the celebrities talking about the movie, with little actual clips of the movie itself. They also tend to recycle actors for unrelated films. Eventually, Dreamworks would reverse this trend and become more selective in their casting choices, much like Pixar and Disney. As shown in the quote on the main page, Chris Rock actually ruffled a few feathers with professional voice actors when he joked during the Oscars that Celebrity Voice Acting is the easiest job in the world.
Pixar doesn't do this as blatantly as DreamWorks, but they are still very guilty of this trope. All of Pixar's films have a cast of familiar faces much better known for on-camera work, assuming they've done any animation at all (beyond Simpsons appearances). Their only adult lead actor to date with extensive voice acting experience is Ed Asner as Carl Fredricksen in Up, and even he is no stranger to live-action, as well as Richard Kind, who played Tom in Tom and Jerry: The Movie but mostly does live-action roles. They manage to avoid flack for this by emphasizing suitability over celebrity; it also helps that their films' advertising doesn't put much, if any, focus on their choice of voice actors. Likewise, the actors who get major roles in Pixar films are usually more well-known and highly respected character actors, rather than up-and-coming celebs or pop stars cast purely to get uninterested audiences into theater seats.
The Disney Animated Canon has a long history of casting well-known musicians, singers, radio personalities, and stage and vaudville actors in their films. With the odd exception here or there they didn't really start to branch out into filmed celebrities until Jeffrey Katzenberg took control of Disney animation in the mid 1980s (tellingy, Katzenberg would leave Disney to create the above-mentioned DreamWorks Animation in the mid 1990s). To this day they continue to use singers, musicians, and Broadway stars in their movies, in addition to film and television stars.
An Unbuilt example: film and vaudeville star Billy Gilbert was cast as Sneezy in Snow White and the Seven Dwarfs (1937). Unlike later examples he was not cast for his star power but rather for his comedic sneezing routines, making this more of a Casting Gag than anything else.
Quite possibly the Ur-Example of this trope as we know it was Pinocchio (1940), which cast popular musician Cliff "Ukelele Ike" Edwards as Jiminy Cricket for the singer's star power. The character proved so popular that Edwards returned to voice him in the film Fun and Fancy Free (1947), as well as in the 1950s version of The Mickey Mouse Club and several short educational films around that time (the I'm No Fool and You Are A Human Animal series).
An interesting case with Saludos Amigos: José "Zé Carioca" Oliveira was a minor pop star before the release of the film in his native Brazil, but the film ended up being his Star-Making Role. By the time the sequel The Three Caballeros was released, he was a full-fledged celebrity in his home country. Caballeros also featured famous Mexican singer, actor, and radio performer Joaquin Garay.
Fun and Fancy Free (1947): actress Dinah Shore narrated the Bongo segment, while Billy Gilbert voiced Willie the Giant in the Mickey and the Beanstalk segment (in a more straight example of this trope than his appearance in Snow White). As mentioned above, Edwards reprises his role as Jiminy Cricket here as well. Edgar Bergen aditionally narrated the Beanstalk segment, though he appeared in live action Framing Device segments for the short as well.
Alice in Wonderland (1951) cast radio personalities Jerry Colonna and Ed Wynn as the March Hare and the Mad Hatter, respectively.
Peter Pan (1953) had noted child star Bobby Driscoll as the title character, along with radio performers Hans Conried and Bill Thompson as Captain Hook and Smee, respectively, though the latter has done plenty of voice work beforehand.
Bob Newhart and Eva Gabor in The Rescuers (1977) and its sequel The Rescuers Down Under (1990). Gabor had previously voiced the female lead in The Aristocats as well. Radio and vaudville personality Jim Jordan also appeared in Rescuers.
Pocahontas had Mel Gibson, who was probably the biggest name that Disney had ever gotten to voice one of their characters (in 1995, mind you). Christian Bale is a borderline example. He was a notable child star at the time but he had not yet achieved his massive worldwide fame. Scottish comedian Billy Connolly likewise has a role, and this was in the midst of his career in the US taking off.
1996's The Hunchback of Notre Dame, with Demi Moore as the female lead and Kevin Kline as her love interest. Notable in that, at the time of her casting, Moore became the highest paid voice actress in history, having earned $10 million for her voice work in the film. The film also included Tom Hulce as the title character, as well as supporting roles from Jason Alexander, Charles Kimbrough, and Mary Wickes (in her last movie role).
2008's Bolt had John Travolta voicing the titular character, though he blended in so well that you really couldn't tell it was him. Miley Cyrus was also in the film as Penny, re-recording all of the dialog previously recorded by Chloë Grace Moretz except for the very first scene where she's younger. Moretz herself is not an example, however, as she had yet to become famous as a live action actress.
Disney also does this outside of the Canon, as shown with their English dubs of Hayao Miyazaki's films - which often cast Disney Channel Kid Com regulars for young protagonists, and Hollywood actors for adult roles - and the Kingdom Hearts series (though the latter also employs many regular voice actors as well, since there is a very large cast of characters).
Butch Hartman's most recent Nicktoon, Bunsen Is a Beast, features the voice of Jeremy Rowler (Lewbert from iCarly) and Ben Giroux (Toddler from Henry Danger).
Bobby Santiago from The Loud House is voiced by Big Time Rush cast member, Carlos Pena. Same thing applies to Ronnie Anne, who was formerly voiced by Breanna Yde (she had various live action roles for Nick).
The miniseries Middle School Moguls is full of Celebrity Voice Actors, since it features the voice of Daniella Perkins, Haley Tju, Lauren Hernandez, Jade Pettyjohn, Jane Lynch, Tim Gunn, Alex Wassabi, and JoJo Siwa.
Kiefer Sutherland and Elizabeth Berkley were Billed Above the Title in order to promote and sell Armitage III. This was during the early '90s, when anime's popularity hadn't quite taken off yet. Minor characters in the movie were voiced by professional voice actors though. They also brought in Juliette Lewis to voice Naomi in the sequel movie.
Dom De Luise was a celebrity before getting into voice acting, being a favorite of Mel Brooks. However, unlike a lot of celebrities, he actually ended up sticking with voice acting for the rest of his life after his first voice acting role as Jeremy in The Secret of NIMH, alternating such roles with other live-action fare.
Phil Hartman, of course, was this when he voiced Troy McClure, Lionel Hutz, and one-shot characters on The Simpsons. He's a bit of a subversion, though. Before his star rose with Saturday Night Live, Hartman already had some voice acting credits under his belt. He just kept it up after becoming famous.
Yet he is considered by some to have run afoul of the downside of this trope with his role as Jiji in Disney's dub of Kiki's Delivery Service, which many fans of the original consider to be wildly miscast. (Unfamiliar viewers and certain critics, on the other hand, found his turn as Jiji to be an unbridled delight.)
Tom Wilson and Mary Steenburgen reprised their roles of Biff Tannen and Clara Clayton-Brown for Back to the Future: The Animated Series. Doc, however, was voiced by Dan Castellaneta. The Telltale games, however, feature Christopher Lloyd himself as Doc Brown (he also played the role in the cartoon's live-action segments, but he was dubbed by Castellaneta).
Hugh Laurie, Mr. Little in the Stuart Little movies, was the only cast member who returned for the animated TV series (though the DVD animated movie does feature the voices of the live-action main cast, including Michael J. Fox).
Mark Hamill has actually become more recognized for being a voice actor than he has for being Luke Skywalker in Star Wars. He moved onto voice acting in the first place because he was failing as an on-screen actor. He's earned particular recognition for his role as The Joker in various media.
The two-part Season 2 premiere guest-stars none other than John de Lancie of Star Trek fame as the premiere's villain Discord, who is essentially Q as a dragon... thing. Although to his credit, he already had plenty of voice acting experience on cartoon shows before starring as Discord. Besides, if you're going to introduce a villain who's basically an expy of Q, who better to cast?
Friendship Is Magic played this straighter in 2014 when "Weird Al" Yankovic guest-starred as party-pony Cheese Sandwich. Yes, he sang. Like John, he also did quite a bit of voice acting before hand.
Season 5 featured a guest spot by Broadway star Lena Hall playing a famous pony pop star. After she mentioned "friendship is magic!" in her 2014 Tony acceptance speech, it was found out she was a huge fan of the show.
The episode "Stranger Than Fanfiction" has Patton Oswalt voicing a character, though he has done plenty of voice acting.
Rooster Teeth tends to avert this when it comes to Red vs. Blue, as the cast consists of members of the Rooster Teeth staff, or lesser-known voice actors such as Shannon McCormick (whom anime fans might recognize as Koroudo Akabane). In fact, when this was played straight with the announcement that Elijah Wood was cast for the role of Sigma, the general reaction was quite a bit of surprise and praise.
The Freakazoid! series finale, "Normadeus", is centered on celebrity carpenter Norm Abram, who voices himself. The voice acting in question is something to behold.
Fairly common in Young Justice. The most prominent examples are Jesse Mc Cartney and Alyson Stoner as Dick Grayson and Barbara Gordon respectively - and even then it's downplayed as voice acting seems to be a secondary career for them. Other straighter examples are George Eads as Barry Allen (Flash), Maggie Q as Wonder Woman, and Bruce Greenwood as Batman. And there are even more examples of this trope in that show.
Garfield and Friends had five of these, all but the first and last limited to the last couple seasons. Howard Morris was Wade Duck, Victoria Jackson was Penelope, stand-up comedian Kevin Meaney was Aloysius Pig, comedienne Imogene Coca was The Fairy Dogmother, and Lorenzo Music - up to that point better known as a TV producer and "on-screen" actor - was Garfield himself.
Worth noting that Morris was a character actor who split his time between on-screen work and voice work, having acted in Hanna-Barbera cartoons for many years prior to Garfield.
A lot of the promotion material surrounding the TV adaptation of Terry Pratchett's Truckers makes a big point of noting that Sir Michael Hordern is a member of the cast, even though his character only appears in 4 out of the 13 total episodes (and in the last of these, he wasn't even alive!). In addition, the lead role of Maskin was Joe McGann,
Most fusions are voiced by famous singers. Garnet is voiced by Estelle, Opal is voiced by Aimee Mann, Stevonnie is voiced by Amanda Joy Michalka, and Sardonyx is voiced by musical theatre star Alexia Khadime. Most notably, Sugilite was voiced by Nicki Minaj... who was too much of a celebrity and thus too expensive to have return, leaving the character to only make two other appearances in the show, both of which are non-speaking.
Sardonyx (after playing a voice clip of Sugilite): She's not... actually in this episode, do we still have to pay her? Yes? Fair enough.
There's also Smoky Quartz, who isn't voiced by a singer, but still by a celebrity: Natasha Lyonne.
Aside from fusions, there was Mr. Smiley who was voiced by stand-up comedian Sinbad, but in season 2 he was replaced by Colton Dunn.
White Diamond and Yellow Diamond get this treatment as well, being voiced by Broadway veterans Christine Ebersole and Patti LuPone, respectively. Blue Diamond is voiced by Lisa Hannigan, which plays with this trope a bit; she has an established music career in Ireland, but is relatively unknown in the U.S., having made a spare few contributions to movie soundtracks and has only done one other voice-over role as Bronagh in Song of the Sea.
When it came time to dub Piccolo, Saxo Et Compagnie (the movie, not the audio record) into English, the producers somehow, despite extreme budget constraints, managed to get their hands on three- Joanna Levesque, the rapper Shad "Bow-Wow" Moss, and Cheech Marin.
G.I. Joe: The Movie features Don Johnson (who was best known at the time for his role as Detective Sonny Crockett in Miami Vice) as Lt. Falcon and the late Burgess Meredith (who starred in the 1945 film The Story of G.I. Joe, which served as the franchise's namesake) as Cobra-La leader Golobulus. Golobulus never showed up again after the movie, while Lt. Falcon had a different voice actor when he returned for the later DiC series.
The title character of the Biker Mice from Mars episode "Hard Rock" was voiced by television and radio presenter Riki Rachtman.
TMNT has Sarah Michelle Gellar as April O'Neil, Chris Evans as Casey Jones, and Patrick Stewart as Max Winters. Kevin Smith also cameos as a diner cook. It's otherwise averted with the rest of the cast having professional voice actors, including the title characters being voiced by James Arnold Taylor (Leonardo), Nolan North (Raphael), Mikey Kelley (Michelangelo), and Mitchell Whitfield (Donatello).
In addition to many of the actors reprising their roles from the movie, Big Hero 6: The Series has used Brooks Whelan as Fred, Katy Mixon and Sophie Reynolds as the mother-daughter villain duo High Voltage, Andrew Scott as Obake, Mara Wilson as Liv Amara, Riki Lindhome as Wendy Wower, Susan Sullivan as Fred's mom, and Jeanne Sakata as Lenore Shimamoto, among others.
While Marvel's Spider-Man largely uses professional voice actors for many of its characters, including Robbie Daymond as the title character, this trope does fall into play for some characters. For example, Sofia Carson voices Keemia Marko/Sandgirl, Nathaniel J. Povin voices Prowler, BooBoo Stewart voices Jack O'Lantern, Cameron Boyce as Herman Schultz, and Ryan Blaney as Overdrive.
The obscure Canadian animated series Zeroman starred Leslie Nielsen as the voice of the eponymous superhero.
Asuka Langley Soryu is voiced by the Irish singer/actress Stephanie McKeon. While she's also known for doing voice acting, albeit exclusively for non-Japanese media until Evangelion, for some Western viewers and listeners, she's known for playing Aisling O'Brien in the Irish TV Soap OperaFair City, her work as a West End actress in London, as well as her relationship with her husband, fellow Canadian singer/actor/composer Kyle Riabko.
Film and TV actor Daniel MK Cohen, known for his work in the LEGO City Adventures series, voices Makoto Hyuga.
Kozo Fuyutsuki is voiced by John Paul "JP" Karliak, best known as the voice of Wolfgang in Skylanders.
Grey in particular was not happy with being replaced due to being a friend and student of the late Mary Kay Bergman, her predecessor as Daphne before her suicide in 1999, and having a personal attachment to the character as a result.
Within the realm of guest stars on the show, David Bowie voiced Lord Royal Highness in "Atlantis SquarePantis" (in one of his last acting roles before his death) and Johnny Depp voiced Jack Kahuna Laguna in "SpongeBob SquarePants vs. The Big One".
The Simpsons has had 833 celebrity guest voices in its' 30-year run, the most for not just every animated show, but every TV show in history and even won a Guinness World Record for this feat. Because of how long it would take to list every single occurrence of this in the show, a general rule of thumb is that if there's a popular celebrity out there and they've done some voice acting, at least one of those roles (or in some cases, their only role) would be a spot on The Simpsons. This is probably because it's seen as a status signal in the world of celebrities, as it shows that the person in question has become a staple of pop culture. As a result of how common this is, The Other Wiki has a comprehensive list of celebrity voice roles on the show.
Disney loved doing this for their Studio Ghibli dubs. In addition to casting well-known names like Cary Elwes and Phil Hartman, they would usually cast celebrities associated with their company like Ashley Tisdale, David Henrie, Noah Cyrus and Frankie Jonas.
The 1997 Cosgrove Hall Discworld cartoons had Christopher Lee as Death. Wyrd Sisters also featured Anette Crosbie, June Witfield and Jane Horrocks as the three witches, Elenor Bron as the Duchess, and Les Dennis as the Fool, while Soul Music had Neil Morrissey as Mort and Graham Crowden as Ridcully.
The end credits song of The LEGO Movie 2: The Second Part features The Lonely Island rapping about reading the credits. Their verse about the voice actors manages to both praise and lampoon the celebrity cast — noting that voice acting in general is hard work and brings humanity to the film, but also that these particular actors are overpaid for comparatively little work.