Keyhole Cichlids, Rainbow Cichlids, Kribensis, Bolivian Rams will go easily as well. Some african species - if you have very hard water (labs and Zebras or Shelldwellers come to mind) - I'm not much help with those though. You could put a single Festivum in there I think. Blue Rams - if you have very soft water, and a good bit of experience with fishkeeping.
You could put a pair of Rainbow Cichlids and a pair of Bolivian Rams. You could put a pair of Keyholes and a single Krib. This would allow you to put a couple of otocinclus in for cleaning purposes as well