I was thinking of some tetras, but wasn't sure whether the dimensions of the tank would be good for them. It doesn't seem like they'd have much back-and-forth room to swim around.
Cherry shrimp do sound interesting. I'll confess to being lazy, though, and would prefer it to be fairly low maintenance. As it is, I've got a 38, 20, and two 2.5 gal tanks to keep happy. I don't mind adding one more to the list, but don't really want to go beyond one or two weekly partial changes on it.