Longhorn Cowfish = the bomb!
If you want really colorful fish, just go to www.liveaquaria.com
and look through the angels and dwarf angels to see if you can find a favorite there. Then check the tangs. There are some really beautiful wrasse as well. These are typically the most aesthetically pleasing fish.
I'm kind of partial to the stranger-looking fish, or fish with funny personalities like the following..
Boxfish (aka trunkfish)
92-gallon corner tank, 100lbs of LR
, 140lbs of sand, 250watt 10,000K MH
, 110watts of actinic PCs, Mag 7 return, custom refugium, AquaC EV180 w/ Mag 5
Female lyretail anthias, eyelash blenny, tomato clown, saddleback clown, firefish goby, 2 sand-sifting stars