Ten gallons gives you a lot of options.
Livebearers such as guppies or platies
Some of the smaller tetras, like neons
Rasboras, like harlequins or anything similar
A single dwarf cichlid
Any shrimp you please, and a lot of them
Or as iamntbatman suggests:
-a small colony of dwarf shelldwellers like Neolamprologus brevis, Neolamprologus multifasciatus, or Lamprologus ocellatus (can be harder to find and a bit more expensive than more common fish but are very interesting and easy to take care of)
Bettas are great, don't knock them. With a ten gallon you could even divide the tank into two or three compartments and keep several. I have a six gallon tank with a betta and four, soon to be six, harlequin rasboras. It's a great little low maintenance tank.