Watch out for hatchetfish, they like to jump. Make sure your tank is well covered, or else you will find little dried up "quarters" with fins on your floor from time to time. Otherwise, they are a very active and fun fish to have.
Kuhli loaches make great bottom dwellers. Very peaceful, unique in shape, and they have lots of personality. The only thing is they like to hide a lot. If you get at least 3-6 though, they will be more active. Give them places to hide, like maybe placing some tiny clay pots on their side in the bottom of your tank. They will curl up in them and declare themselves hid, even though you can see them in there.
Tetras make great mid fish. I'm partial to neons. They are colorful and fairly cheap.
Otocinclus are also cute little fish, and they do a good job on algae. They also stay small, so you dont' have to worry about a big bioload from them.