daddypa
Grayce
Graycie
Grayman
Grayp's (Gray Puss)
Gray-Puss
Grayson
Graystoke
Grayus Kitty Cattus
Graza
Grazie
Grazzi
Grease Monkey
Greased Lightning
Greasy
Great Pet
Great Spud Wombler
Greatest Hits
Great-Grandma
Greco
Gredie
Greebo (after the witch's cat in the Terry Pratchett discworld novels)
Greebo (cat in the Discworld novels)
Greedy
Green Eyed Monster
Green-Eyes
Greeny Gerocious
Greg
Gregarious Gizmo
Gregory
Gregory the Great (Pope from 590)