What boss mechanics would you like to see again, in one form or another, in the Cataclysm raids? Obviously the mechanics shouldn't be carbon copies of the originals, but at least something similar to them. So, what mechanics would you like to see again, and why?
Kara Chess encounter: While this was pretty much a free loot encounter, it was still a fun and refreshing change of pace from the rest of the raid.
Heigan Safety Dance: This was fun for the most part since it required your raid to focus more on movement than on pure DPS. The only downside was that people with slow computers or alot of lag had a hard time surviving.
Voljasz's Hallucinations: While not a raid boss, he still had a very cool mechanic. Having to defeat evil hallucinations of your party members was cool and original.
Gruul's growths: This was a DPS race not because he would enrage or overwhelm you with adds, but because he would eventually become so strong that he would simply obliterate your tanks.
Lana'thel's bites: You become a vampire and do tons of damage while generating no aggro, but you have to bite someone else before you become MC'd. On paper it's a relatively simple mechanic. In practice, you'd be amazed by how many people fuck this up.
Occulus drakes - Most people hated Occulus, but I loved it. The drakes were very cool and allowed you to perform a role you don't ordinarily perform in a group. A Cataclysm version of this could have players becoming empowered with one of the four elements, gaining unique abilities with each element.
There are probably more I'd like to see, but these are the only ones I can think of off the top of my head.