On a positive note. Some LFS will exchange or credit you for your current fish. In that size tank a trio (2 females 1 male) of fancy guppies or dwarf platys, or a nice school of cardinal or neon tetras. You could also try to find some golden white clouds. I'd think with just a trio or a school of 6 small fish you could add in some shrimp, or an African dwarf frog. They are really fun and colorful, and have a minimal affect on the bio-load. Just be sure it's a DWARF frog because the clawed ones get really big.

There really are a lot of options for small tanks. A male Betta and a school of tetras would be really colorful. Hard to judge Betta temperament, but I have one with my community fish and he does great.

Other small but very colorful fish to consider
Frankenfish - otherwise known as glofish
Marble Hatchet fish - really pretty in schools too
Rummy nosed tetras - only a few though
Rosy Tetras - really lil fishes
Exotic Shrimp - again that's a perfect size tank for these new and very popular inverts. I've heard they breed like crazy.

Best of Luck.....And overloading is one of the things I have to really work on too. I just got my tank back to a reasonable load. I helped use my extras to start a 10 gal for a friend.