If this is an established tank, what fish do you already have?
Many of the larger angels will pretty much rule a tank, but you need to be cautious adding one if you already have large established fish.
Emperors are nice and IMO, worth the money. Blueface are gorgeous, relatively hardy but shy. Same with majestics that stay a bit smaller. IME, they do best when they are the alpha fish in the tank. Place them with bullies and they can go south.
Other choices include the Koran, Queen (very aggressive), Cortez, to name a few,
If you want something a bit out of the ordinary, look at some from the chaetodontoplus genus. The Scribbled is beautiful.
Try to get something in the 3-5 inch range. A bit hardier and can hold it's own. Don't add any angel unless the tank is mature (6-8 mos) with consistantly good water and lots of live rock.