You could try a bamboo shrimp, they get big and are great filter feeders. Might be worth the try since they are cheap and when they are full grown can be very impressive. If you get a decent sized one at a LFS your angels shouldn't bother it. They are a cichlid so you have been warned!
Progression of my 55 Gallon (Beware lots of pictures!)
Just an update! Had an algae issue, made some changes and heres where I am at! Still digging it. I also added some new inhabitants! Several more otos, 7 nerite snails, added a female blue ram, changed out the shoaling fish to Serpae tetras, and sold 2 angels.
55 Gallon Planted
3 GBR, 2 Bolivian Rams, 1 Juvenile Super Red BN Plecos, 9 Oto Catfish, 9 Bloodfin Tetras
Rotala Indica, Cardamine, Crypt Spiralis, Pygmy Chain Swords, Dwarf Sag, Lutea Crypt, Wendtti Bronze and Red, and Floating Frogbit