I have a handfull of ember tetras in there. They're ok, but I just found out a local shop has a decent selection of rasboras and other micro fish. I wish I had seen them first!
I'm also tempted to put a crayfish in there, but I'm worried about the plants. I've heard they'll shred the plants.
You could get a Dwarf Orange Crayfish, they're pretty mellow. Just like a shrimp but a crayfish. I'd advise against a crayfish any larger, mine destroyed every plant, ripped my snail out of its shell, pushed the driftwood into my barb (killing it), then climbed out and decimated my Lucky Bamboos roots, dropped back in and ruined part of my Mangroves roots, then for the final she climbed out crawled around under my bed, onto my bed, and then finally decided I'd be delicious.
Needless to say she's in an escape proof 32 gallon that's only hardscape.