Not many fish are suited to live in a tank that small. You can do a betta and a few pigmy cories, or one dwarf puffer. I've also heard of keeping a few guppies (all one sex) in there. That tank is definately too small for angels, they need atleast 30 allons.If you do a betta, make sure you have some plants near the surface that he can lay on, as bettas aren't very strong swimmers. If you go for male guppies, make sure you have many decorations in the tank to help ease agression issues.
Also, have you read about cycling the tank? I'd strongley recomend a fishless cycle, as cycling can be harsh on the fish. If you decide to only keep a betta in there, you can leave the tank un-cycled and just do frequent water changes