Galsky, Melissa Bardin
Melissa on Home Movies, Lucy on Lucy, Daughter of the Devil, etc.
Garrett, Brad See actors E-G
Torque Armada on Buzz Lightyear; Fatso in Casper; Eeyore in Christopher Robin (which I haven't seen yet); Magmanamus on Dexter's Lab; Bloat in Finding Nemo; the Giant in Hoodwinked Too!; Bubbles in Michael Jackson's Halloween; Noah on Project G.eeK.eR.; Eeyore in Ralph Breaks the Internet; Bibbo and Lobo on Superman and Justice League; Jim Rage in the mustache ep of The Tick; etc.
Giamatti, Paul See actors E-G
Title character in The Amazing Screw-On Head; Stan Beals in The Ant Bully; Drek in Ratchet & Clank; Tim the gate guard in Robots.
Gilbert, Melissa See actresses G
Batgirl on Batman: The Animated Series.
Winry on Fullmetal Alchemist, Triela on Gunslinger Girl, Vivi on One Piece (FUNi dub), Miss Anderson on Shin chan, Wendy on Trinity Blood, etc.
Goldberg, Whoopi See actresses G
Shenzi in The Lion King, the White Rabbit's wife in an episode of Once Upon a Time in Wonderland, Yakult in an episode of Suburgatory, Stretch in Toy Story 3.
Goldthwait, Bobcat See comedians
Gary in an episode of Bob's Burgers, XL on Buzz Lightyear of Star Command, Pain in Hercules.
Goodman, John See actors E-G
Pacha in the Emperor's New Groove franchise; Robot Santa Claus in an episode of Futurama; the original voice of Yellow in M+Ms commercials (replaced by J.K. Simmons); Sulley in the Monsters, Inc. franchise; Mr. Prenderghast in ParaNorman; Big Daddy in The Princess and the Frog; Grim in Ratchet & Clank.
Gottfried, Gilbert See comedians
The duck in a bunch of AFLAC commercials, Iago in the Aladdin franchise, Mr. Greenway in Elf: Buddy's Musical Christmas, Mr. Mxyzptlk in a couple eps of Superman, etc.
Grammer, Kelsey See actors E-G
Vladimir in Anastasia; the title character on Gary the Rat; Narrator of an episode of Just Shoot Me!; Tin Man in Legends of Oz: Dorothy's Return; Sideshow Bob in numerous episodes of The Simpsons.
The title character on Daria.
Griffin, Grey See DeLisle, Grey
Usopp on the 4Kids dub of One Piece, Cilan, Brawly, Looker, et al. on Pokemon.
Wakko on Animaniacs, Fatso in Casper Meets Wendy, Captain Hero et al. on Drawn Together, Piecemeal on The Secret Saturdays, Odin, Hercules, et al. on Super Hero Squad Show, Sewer Urchin et al. on The Tick, Jerry on Totally Spies!, etc.
Hartman, Phil See actors H-K
Jiji in Kiki's Delivery Service, Lionel Hutz and Troy McClure on The Simpsons, etc.
Aizen and Ganju on Bleach, Ox-King and General White on Dragon Ball, adult Gohan, Narrator, et al. on Dragon Ball Z (FUNi dub), Vato Falman on Fullmetal Alchemist, Kamina on Gurren Lagann, Peta on MÄR, Omega-Xis on MegaMan Star Force, Fritz Vardemann on Monster, Jiguro Musa on Moribito, Kiba et al. on Naruto, Professor Oak on Pokemon Origins, etc.
Hill, Amy See actresses H
She voiced Tohru's mother on Jackie Chan Adventures; and Jasmine Lee (Ah-Mah) on The Life and Times of Juniper Lee; etc.
Hong, James See actors H-K
A couple eps of Avatar: The Last Airbender (Mayor Tong in "Avatar Day" and Dour Monk in "The Storm"); Dalong Wong on Jackie Chan Adventures; Mr. Ping in the Kung Fu Panda movies; Chi-Fu in Mulan; Mandarin on Super Robot Monkey Team Hyperforce Go!; etc.
Jane, Helen, and Quinn on Daria.
Hudson, Bella (aka Erica Schroeder)
Bridget on Mew Mew Power, Luffy in the 4kids dub of One Piece, Nurse Joy (season 6-8), Bianca, Fantina, Kenny, Shelly, et al. on Pokemon, etc.
Hurt, John See actors H-K
The Horned King in The Black Cauldron; Professor Bruttenholm in Hellboy: Blood and Iron; Narrator in The Tigger Movie; etc.
Irons, Jeremy See actors H-K
Scar in The Lion King.
Isaacs, Jason See actors H-K
Zhao on Avatar: The Last Airbender, Sinestro in Green Lantern: Emerald Knights.
Iwamatsu, Makoto See Mako