You could go for the gold and get a bull snake, bigger than any king but still kind of medium sized. The whited sided bulls are AMAZINGLY pretty. Gopher snakes are pretty rad too.
Everglades, bairds, black, yellow, texas, trinket, radiated...um....I know there's more but those are all rat snakes you could look into. Bairds are my favorite. Red tailed, blue beauty, and mandrian rats are good looking snakes, but I hear a little temperamental.
I like the axanthic florida kings best of all king snakes, the mexican blacks are pretty too.