New standard UI: Looking for Dungeon, Quest Tracking

http://www.wowhead.com/?guide=3.3&ui

The biggest UI changes in this patch is, without doubt, the new Looking for Dungeon (LFD) system. In some ways it is only a big improvement over the old LFG/LFM one, but in many ways it's a revolutionary change over it. It allows for relatively quick group assembly, that includes players from multiple realms. The game uses players' input to determine who will play the role of tank, healer, or DPS, in case more than one member of the group are capable of performing two of those things. It also teleports players straight to the dungeon - summoning stones are about to become very obsolete!

The other UI changes that should be mentioned are the improved quest interface and the changes to nameplates visibility. As soon as both features are complete, players will be able to track quests on the world map, as well as make large packs of mobs display their nameplates on the screen in a more... civil manner, not hiding every single pixel behind a wall of red health bars and names.