The only fish I'd recommend for that size tank would be a single betta or a group of algae shrimp. Both would need a heater and filter (bettas can go without filters so long as you keep up on water changes, but it's a lot more work) and would appreciate live plants.
If you want to keep more fish of different varieties in a community tank, I'd save up and buy the biggest you can afford, at about 20+ gallons you can start to get a decent community tank going, anything smaller is difficult to stock and maintain.