(woohoo, first post)
I've got a trio of Dario dario ("Scarlet Badis") in a 5.5 gallon setup. they can be finicky eaters at first, but generally are easy to care for. Give them peaceful tankmates (cherry or similar shrimp are ideal) and they do great, and do especially well in heavily planted setups. Good luck finding females without going through a breeder though... All three of mine are males, and the only LFS within several hours that can even get them never has been sent females from his supplier.
My favorite of my three is attached