Mine is heavily stocked... you can see my critters in my signature. I have 3 green chromis, and they're fine together (so far).
Other good choices would be a mated pair of clowns... ocellaris are my favorites. You could also add a royal gramma, a goby and/or blenny, fire fish, cardinal fish, yellow coris wrasse, pygmy hawkfish... or take your chances with a pygmy angel.
Lots of great options! You could even do a damsel or two... just be careful with tank mates and add them last.