www.lodidodi.net
Best priest UI ever IMO, and probably excellent for other classes as well. Changing HP color guages, clickable items and inventory easily accessible without taking up tons of room, text to the side of spells and buffs (without being in the way), a pink casting line under the target window, % next to all HP and mana displays... etc.. all make this a very nice cleric UI.
Of course my windows and layout are set up differently, but that is my opinion of what an ideal priest UI would contain.