Ok, I am gonna recommend a few fish that no one here has recommended. I like being a little different.
1. You could try the least killie Heterandria formosa (smallest live bearer). Females get about an inch and half, while the males are under an inch. You can keep about a dozen in a 5 gallon tank, just make sure it is heavly planted.
2. a pair of pygmy sunfish, either Elassoma zonatum or Elassoma okeefenokee. But this would be a tank for the more advanced aquarist. These guys need live food. But they are very pretty and would make an interesting and different tank.
3. How about a Paradise fish. These are cheaper than Bettas. I find them more striking in coloration. I currently have one in a 2.5 gallon aquarium. This guy has the most personality of any fish I ever had. He is fully aware of everything that goes on here at my desk at work.
I also recommend with what ever you have, Malaysian Trumpet Snails. They are a great cleaner for substrate and the sides. I also keep ghost shrimp.
jim