Creature
Creeper
Creme
Creola (named for the Jimmy Buffett song)
Crescent
Cresent
Crestone
Crichton (from the J.M. Barrie play "The Admirable Crichton")
Crick
Cricket
Criendger
Crier
Criffin
Crimson
Cringer (after the tiger in the "He-Man" cartoon)
Cris
Crisco
Crispy
Crisslynn
Crissy Cat
Cristyl
Critter
Critters
Crockett
Crocus
Croissant
Cromwell
Crookshanks (Hermione's cat in the Harry Potter books)
Crooksy
Crosby