Cory cats are the absolute best cleaning crew out there IMO so if you build your stock around them(not too aggressive) they would be great. Others that are neat: synodontis sp., Raphael cats, sun cats, pictus cats, various plecos, and more.
I have a couple spotted head bullheads in my 55g an I love them. They only come out at night but they stay under 8 or 9" and won't be eaten by other fish.