Sanctifikitty
Sand Rat
Sanders
Sandie
Sandler
Sandler (after the actor Adam Sandler)
Sandman
Sandoval
Sandra
Sandrake
Sandrine
Sandunga (from a Mexican song)
Sandy
Sandy Claws
Sandy Koufax (after Sanford Koufax, baseball pitcher)
Sangievese
Sangria
Sanspoof
Santa
Santa (after the novel by Federico Gamboa)
Santa Fe
Santal
Santana
Santaria
Santa's Little Helper
Santi
Santi (aka santi claws, a found cat who had been stuck in a chimney 4 days)
Santini
Santo
Sanura (Egyptian for "pretty little girl in a field of flowers")