Important WoW Raiding Addons

The main aim at level 80 is to clear the end game content. There are many addons out there that will assist you in doing this and will make it easier to assess your own performance and the performance of others.

Deadly Boss Mods
Having an addon like this is key to making sure you don't fail. Deadly Boss Mods gives you important information during boss fights like when the next phase begins or when adds are spawning or when the boss is going to use a special ability. The advantage of having this is that you can prepare for the next step like on Anub you could get to the centre ring a bit quicker or on Sapphiron you could move away from the boss earlier to make it easier to get behind an ice block. It also records how long your fights have taken and you can compare how your group has done with previous weeks. On top of all this it isn't very memory consuming.

http://www.wowinterface.com/downloads/info8814-DeadlyBossMods.htm