I also don't bother with filters on mine - only 10g and up get filters (not eough outlets for everything). I know there is the tetra 3i and the small world filter that are both supposed to be for small tanks. Never used either one though.
you need an airpump and tubing
If it ws me, I would just pay the $15 and get a 5 gallon. Then you can cycle it, supposedly smaller tanks can cycle, but eh, I don't think it would be worth it.
Originally not even the 10's had filters. My apt was old and not in good repair when I lived in Alaska. I though I might start an electrical fire if I had too much stuff plugged in. Oddly enough, the day I was to move out, the apt that was the furthest away from me did have an electrical fire.