a couple or three dwarf gourami's might be ok if you keep the water clean.
or there's always the old standby, the betta (who would love that size of tank!)
small school of guppies?
or for some real fun, fill it partway with water, get a good cover, and put some fiddler crabs in it. fiddlers are cool (IMO), just make sure you give them a rock to sit on thats out of the water.....
if you put a 2 males and 1-2 females, the males will dance and pose to impress the females