Are you wanting it to still be a coldwater tank, or are you ok with going tropical?
If coldwater, ten gallons have pretty few options. A dwarf crayfish(they, or some types, may need tropical waters though, I can't remember for sure), maybe some smaller types of shrimp. Cloud minnows would be a might, I don't know if they can be in tanks that small.
If you wanna go tropical you could get a betta, or three African Dwarf Frogs, or turn it into a shrimp tank again for critters like Cherry Shrimp, ghost shrimp, amano shrimp and the like. You could get 4-5 guppies or 5-6 Endlers. Some dwarf rasboras are a might, but again you'd have to check and see if ten gallons is too small.
Those are all the ideas I can think of off the top of my head.