angel fish
I think its way too small for angels. the dimensions make it about a 10g tank.
You might be able to get away with apistos, but that footprint is really not ideal as its a tall tank.
If it were mine, I would do invertebrates or microfish (small tetras, rasboras, or a small rainbow species).
I just picked up some from Rachel and they're fun guys to watch. Very colorful and active.I carry scarlet badis as well