Has anyone mentioned pygmy killies (Leptolucania ommata) or bluefin killies (Lucania goodei) yet? The bluefins would need atleast a five gallon for a pair, but a pair of pygmy killies could easily be housed in a 2.5 gallon. American Aquarium Fishes says a pair can be kept in a 1 gallon jar that's filled with java moss. The three legal Elassoma species (pygmy sunfish) would also be good for a 5 gallon or larger. A 2.5 might work, but they're a little on the aggressive side so I would go with a five. The other three are protected, but the three that are legal are absolutely beautiful fish. The legal ones are E. okefenokee, E. evergladei, and E. zonatum. Another good fish is the swampfish, Chologaster cornuta, if you can find them. I think jonahsaquarium.com has them available. All of these fish come from swamps that have lush aquatic vegetation and will all readily spawn in the aquarium, except for the swampfish, which I believe may have only spawned once in captivity, if that.