You would be fine with a community tank of tetras (many options: white skirt, black skirt, phantom, cardinal, neon, penguin), corydoras are awesome (just get a small variety such as pygmy and panda), and you could also get livebearers (swordtail, molly, guppy). I also have a 15 gallon (long) tank with 5 tiger barbs. They are very healthy and always schooling together. Very active fun fish, just don't put them with slow moving fish, they are fin nippers). Have Fun!