erm you could have all manner of platys and sword tails, get a small shoal of either one colour, or mix it all up,
some smaller bottom dwellers such as dwarf cats and corys. maybe dwarf cichlid like the nanacara sp.
all types of small characins like tetra's
anything you want really providing it dosnt get to big
edit- personaly id like to have a big shoal of tetra in there, maybe neons, but i know they can be expensive for a large group
