- Greg Eagles
- Â Grim / ... 71 episodes, 2003-2007
- Richard Steven Horvitz
- Â Billy / ... 71 episodes, 2003-2007
- Grey Griffin
- Â Mandy / ... 71 episodes, 2003-2007
- Vanessa Marshall
- Â Irwin / ... 55 episodes, 2003-2007
- Jennifer Hale
- Â Billy's Mom / ... 41 episodes, 2003-2007
- Jane Carr
- Â Pud'n / ... 30 episodes, 2003-2007
- Rachael MacFarlane
- Â Mindy / ... 30 episodes, 2003-2007
- Dee Bradley Baker
- Â Mandy's Dad / ... 26 episodes, 2003-2007
- Renee Raudman
- Â Ms. Butterbean / ... 20 episodes, 2004-2007
- Phil LaMarr
- Â Irwin's Dad / ... 18 episodes, 2003-2007
- Chris Cox
- Â Principal Goodvibes / ... 16 episodes, 2005-2007
- Maxwell Atoms
- Â Jeff the Spider / ... 13 episodes, 2003-2007
- Tom Kenny
- Â Wiggly / ... 11 episodes, 2003-2007
- Steve Blum
- Â Announcer / ... 11 episodes, 2004-2007
- Armin Shimerman
- Â General Skarr / ... 10 episodes, 2004-2007
- Frank Welker
- Â Anchorman / ... 9 episodes, 2004-2007
- Diedrich Bader
- Â Hoss Delgado / ... 9 episodes, 2003-2007
- Bart Flynn
- Â Bear / ... 8 episodes, 2004-2006
- Roger Rose
- Â Announcer / ... 8 episodes, 2003-2007
- B.J. Ward
- Â Baby / ... 7 episodes, 2004-2007
- Debi Derryberry
- Â Nergal Jr. / ... 7 episodes, 2003-2007
- Billy West
- Â Announcer / ... 7 episodes, 2003-2006
- Quinton Flynn
- Â Announcer / ... 6 episodes, 2003-2006
- Cam Clarke
- Â British Captain / ... 6 episodes, 2003-2005
- Peter Lurie
- Â Alien / ... 6 episodes, 2003-2007
- Peter Renaday
- Â Abraham Lincoln / ... 6 episodes, 2003-2005
- Martin Jarvis
- Â Nergal / ... 6 episodes, 2003-2007
- John Kassir
- Â Lord Moldybutt / ... 5 episodes, 2004-2007
- Julian Stone
- Â Sir Raven / ... 5 episodes, 2004-2007
- Jess Harnell
- Â Singer / ... 5 episodes, 2003-2007
- Brian Cummings
- Â Anchor / ... 4 episodes, 2005-2006
- Greg Ellis
- Â Another Astronaut / ... 4 episodes, 2004-2007
- Amber Hood
- Â Sassy Cat / ... 4 episodes, 2005-2007
- Bob Joles
- Â Cheese Puff Dealer / ... 4 episodes, 2004-2006
- Fred Tatasciore
- Â Aztec Ghost / ... 4 episodes, 2005-2007
- Dwight Schultz
- Â Criag / ... 4 episodes, 2004-2006
- Pat Fraley
- Â Announcer / ... 4 episodes, 2004-2006
- Rob Paulsen
- Â Creature / ... 4 episodes, 2003-2007
- Scott Menville
- Â Couple / ... 4 episodes, 2003-2006
- Jake Thomas
- Â Nigel Planter 4 episodes, 2003-2007
- Michael Gough
- Â CIA Agent #6 / ... 4 episodes, 2004-2005
- Nolan North
- Â Ah Yeah Man / ... 3 episodes, 2006-2007
- Gregg Berger
- Â Bookworm / ... 3 episodes, 2003-2007
- Bill Farmer
- Â Blort Sportscaster / ... 3 episodes, 2004-2006
- Henry Gibson
- Â Lord Pain 3 episodes, 2004-2007
- Keith Ferguson
- Â Creature / ... 3 episodes, 2006
- Patric Zimmerman
- Â Beetle / ... 3 episodes, 2005-2007
- James Arnold Taylor
- Â Announcer / ... 3 episodes, 2004-2006
- Dave Wittenberg
- Â Harvey / ... 3 episodes, 2005-2007
- Jodi Benson
- Â Blue Fairy / ... 3 episodes, 2004-2006
- John Vernon
- Â Warden Toadblatt 3 episodes, 2003-2005
- 'Weird Al' Yankovic
- Â The Squid Hat 3 episodes, 2003-2005
- Dorian Harewood
- Â Burrito / ... 2 episodes, 2004-2007
- Jim Cummings
- Â Nasalmancer / ... 2 episodes, 2005-2006
- Barry Dennen
- Â Blubbery Joe / ... 2 episodes, 2006
- C.H. Greenblatt
- Â Fred Fredburger / ... 2 episodes, 2006
- David L. Lander
- Â Brain / ... 2 episodes, 2004-2007
- Dawnn Lewis
- Â Girl #2 / ... 2 episodes, 2005-2007
- Tara Strong
- Â Girl / ... 2 episodes, 2005-2007
- Jill Talley
- Â Jason / ... 2 episodes, 2004-2005
- Kari Wahlgren
- Â Hariel / ... 2 episodes, 2007
- Fred Willard
- Â Boogey / ... 2 episodes, 2004-2007
- Nika Futterman
- Â Maxwell Atoms / ... 2 episodes, 2006
- Jeff Doucette
- Â Admission Ghoul / ... 2 episodes, 2004-2005
- Alan Oppenheimer
- Â Father Time / ... 2 episodes, 2003-2006
- Tom Kane
- Â Cap'n / ... 2 episodes, 2004-2005
- Kevin Michael Richardson
- Â Corn Vendor / ... 2 episodes, 2003-2005
- Candi Milo
- Â Grim's Mom / ... 2 episodes, 2004-2007
- Danny Mann
- Â Bicycle Guy / ... 2 episodes, 2004-2007
- Ronnie Schell
- Â Real State Agent / ... 2 episodes, 2004-2007
- Kurtwood Smith
- Â Grim's Dad 2 episodes, 2004-2006
- Wayne Knight
- Â Jack 1 episode, 2003
- Robin Atkin Downes
- Â Chocolate Sailor #2 / ... 1 episode, 2004
- Joan Van Ark
- Â Mandy #3 / ... 1 episode, 2004
- Malcolm McDowell
- Â Baron Von Ghoulish 1 episode, 2005
- Thom Adcox-Hernandez
- Â Nerd #2 / ... 1 episode, 2005
- John Cygan
- Â Man at Police Station / ... 1 episode, 2004
- Carol Kane
- Â Mrs. Claus 1 episode, 2005
- Charlie Adler
- Â Lubbermouth / ... 1 episode, 2005
- Susanne Blakeslee
- Â Crabina / ... 1 episode, 2005
- Louie Anderson
- Â Burt 1 episode, 2006
- Mary Jo Catlett
- Â Witch 1 episode, 2004
- Earl Boen
- Â Doctor / ... 1 episode, 2004
- Michael Lindsay
- Â Bobby 1 episode, 2004
- Gilbert Gottfried
- Â Santa Claus 1 episode, 2005
- Michael Bell
- Â Bunny #1 / ... 1 episode, 2005
- Charlie Brill
- Â Irwin's Grandpa / ... 1 episode, 2006
- Jeff Bennett
- Â Alien #1 / ... 1 episode, 2007
- David Berón
- Â Climber / ... 1 episode, 2007
- Michael Dorn
- Â Clown / ... 1 episode, 2004
- Paul Eiding
- Â Barney / ... 1 episode, 2004
- Jennifer Darling
- Â Pollywinkle 1 episode, 2005
- Hamilton Camp
- Â Country Dirty Gnome / ... 1 episode, 2006
- Parul Mercier
- Â Coronado / ... 1 episode, 2007
- Alastair Duncan
- Â Head / ... 1 episode, 2004
- Jim Ward
- Â Dr. Ted / ... 1 episode, 2004
- Kath Soucie
- Â Bear / ... 1 episode, 2005
- Billie Hayes
- Â Granny Applecheeks / ... 1 episode, 2005
- Rip Taylor
- Â Larry 1 episode, 2007
- R. Lee Ermey
- Â Drill Sergeant / ... 1 episode, 2004
- Bill Fagerbakke
- Â Clerk / ... 1 episode, 2005
- Richard McGonagle
- Â Father Time / ... 1 episode, 2005
- Pat Musick
- Â Female Pony / ... 1 episode, 2005
- George Dzundza
- Â Coach 1 episode, 2006
- Masasa Moyo
- Â Tanya 1 episode, 2007
- Joher Coleman
- Â Monk 1 episode, 2007
- Phil Proctor
- Â Cornea / ... 1 episode, 2004
- Dave Fouquette
- Â Bruce / ... 1 episode, 2004
- Josh Keaton
- Â Driver / ... 1 episode, 2005
- Rino Romano
- Â Guillermo / ... 1 episode, 2005
- Bob Thomas
- Â Nigel Planter's Dad 1 episode, 2005
- Mr. Lawrence
- Â Alien #2 1 episode, 2007
- Lara Jill Miller
- Â Girl / ... 1 episode, 2004
- Jason Spisak
- Â Goblin / ... 1 episode, 2005
- Andrea Martin
- Â Monster Wife 1 episode, 2006
- Andrew Kishino
- Â Player #41 / ... 1 episode, 2006
- Jim Rash
- Â Announcer / ... 1 episode, 2004
- April Winchell
- Â Kid / ... 1 episode, 2007
- Mako
- Â Narrator 1 episode, 2004
- April Stewart
- Â Scorpion Mom / ... 1 episode, 2006
- Michael McKean
- Â Kalgoron 1 episode, 2007
- Andre Stojka
- Â Basil / ... 1 episode, 2006
- James Sie
- Â Plain Cow 1 episode, 2007
- Edward Asner
- Â Mr. Voorhees 1 episode, 2003
- David Warner
- Â Nergal 1 episode, 2003
- Mark Hamill
- Â Co-host / ... 1 episode, 2003
- Betty White
- Â Mrs. Doolin 1 episode, 2003
- Keone Young
- Â Quan Ti 1 episode, 2003
- Victoria Carroll
- Â Judge 1 episode, 2003
- James Horan
- Â Cowboy / ... 1 episode, 2003
- Jeannie Elias
- Â Malaria 1 episode, 2003
- Paula Tiso
- Â Atrocia 1 episode, 2003
- David Ivie
- Â Grim (singning) 1 episode, 2003
- Christopher Lloyd
- Â Snail 1 episode, 2004
- Mary Gross
- Â George's Wife / ... 1 episode, 2004
- Cree Summer
- Â Cave Witch 1 episode, 2004
- William Daniels
- Â Scythe 2.0 1 episode, 2005
- Jim Meskimen
- Â Chubby Employee / ... 1 episode, 2005
- Lori Alan
- Â Girl #2 / ... 1 episode, 2005
- Ian Abercrombie
- Â F 1 episode, 2005
- Jack Angel
- Â Master Control 1 episode, 2005
- Dan Gilvezan
- Â Businessman #1 / ... 1 episode, 2005
- Mitzi McCall
- Â Nanny 1 episode, 2006
- Jay Gordon
- Â Sick Guy / ... 1 episode, 2006