A while ago the Macintosh version of World of Warcraft got inbuilt movierecording. At that time I was in hardcore guild raiding 4 or 5 nights a week, I have since scaled down my playing time massively and only play 2 nights a week or so in a very casual guild.
One of the most interesting fights in WoW at this moment is Prince Kael'Thas Sunstrider. Kael'Thas is the final boss in Tempest Keep: The Eye, a 25 person raid-dungeon. The fight consists of 5 distinct phases, all have to be executed to near perfection with at most 1 or 2 deaths before phase 4 kicks in. The fight lasts for a total of about 15 minutes, with little to no breaks in between the phases (depending on the damage output of your raid).
In Phase 1 you fight his 4 advisors, one at a time.
In Phase 2 you fight the weapons of the advisors, the weapons can be picked up when they "die" and these give special abilities when clicked, such as resistance to stun effects or when equipped, such as increased resistance to magic damage.
In Phase 3 the advisors are brought back from the dead and you have to kill them again, this time all 4 at the same time, you might have 1 weapon still left alive.
In Phase 4 Kael'Thas himself becomes targetable, he occasionally summons phoenixes, these die by themselves but once they die they turn into an egg, you need to kill this egg otherwise a new phoenix spawns and you might end up with 2 or even 3 phoenixes, which would mean death on a massive scale. The Phoenixes need to be kept away from the main body of the raid as they do a generous amount of fire damage to all around. Ideally you enter phase 4 with only 1 advisor still left alive. Kael sometimes uses a shield ability that when it fades does large amounts of damage to all around, the key here is to burn down the magic shield and prevent him from using the fire blast ability as it one-shots your tank which leads to a wipe.
Phase 5 is more of the same thing, only Kael'Thas stops using his fireblast ability and instead occasionally causes a gravity lapse, sending everyone flying in the air. Whilst in the air you can swim to a safe spot, as you do not want to be too close together for some other abilities like a sort of chain lightning.
If you're interested you can view a detailed strategy guide on Bosskillers and you'll see I skipped over quite a lot of the details.
Because of the complexity of the fight learning the encounter takes a while, especially the first days can be gruelling as even one or two deaths means you might as well all suicide and have a fresh start. Ideally you lose no one in phase 1 and 2 and 3. Once you enter Phase 5 you're basically home free and you can finish the fight as long as you have about 15 people alive. Needless to say killing an end boss that needs such refined tactics means you do not simply level to 70 and have a go at him, there is quite a way to get to him and you only want to bring people with excellent gear and the ability to work together.
Anyways, I created a movie of the fight and thought I'd post it here for you all to see. The movie is hosted on Filefront and you can view it as a streaming flash thing or click the download button and get the divx file if you have a player such as VLC.
As you can see the room where we fight Kael'Thas is rather large which is a good thing for Phase 3 where you have lots of things going on at the same time.
I play a druid in WoW, he's always in the middle of the screen on the movie above, I start off in humanoid form but often shift to tree-form, which gives better and more efficient healing output. The nice thing of the mac movie recording feature is that it also captures the sounds in-game so if you hear a lot of grunting that is from the bosses being hit on da hed.