A very nice, hearty and inexpensive angel for a tank that size is the grey poma (black velvet), I just picked up a beautiful juvenile for under $30, the only affordable member of the genus and although not a stunner like some angels I think the adults are just beautiful and they have a great personality and lack the aggressiveness of other angels. The kole is a great tang for a tank that size and very beautiful as well. Butterflies are all over the board in terms of size and heartiness but I have found the raccoon to be both gorgeous and tough.