a Blue Spotted Angel, a Black Velvet Angel (Gray Poma), a Vermiculated Angelfish (Singapore Angel), a Multibarred Angelfish (Manybanded Angel), a Venusta Angel (Purple Masked Angel), and basically any dwarf .. and besides all the dwarves .. some of those angels I mentioned may be hard to keep .. research them before you buy them but I think that you could keep any of those I mentioned full grown in a 55 gallon