How about some midsized schooling fish...some type of tetra. YOu could put a nice large group of one of those in there and I think that would look great.
Pick a schooling fish that's not too colorful, since you don't want them to overshadow your angels. I have some prestella tetras that I think are very nice for that reason. Their body color is muted but they have these very bright yellow/black "tags" on thier fins that really stand out....but not so much as to visually "take over" my tank. I believe they're large enough too, that the angels wouldn't make a snack of them....lol....but my angels haven't yet reached full size, so I have to wait and see.
