Well I'm totally in the nostalgia sector here. Really nice reading up on those good ol' boss fights. There was a lot of good fights imo.

Favorites for 5 man is:

Van Cleef. Just because it was my first taste of a boss (yes, WoW was my first MMOG). Then again, the whole deadmine instance is great to me just because of this factor.

High Inquisitor Whitemane! Such a great fight, compared to the others at the time. And for some reason I love clearing up to the fight. Again, the instance itself was soooo good. And the loot she had! Daum. Such awesomeness. I had both her hammer and her chapeu (I was a priest).

Then there's Princess Theradras. Still remember the first time I got afflicted by that bunny-jump effect. In retrospec, I think the boss was perfecty tweaked for PUGs of those time. People hadn't quite gotten used to scripted fights, and had some problem co-operating, but still managed to get the concept more and more. I don't think I could count the amount of times me and the PUG barely made it.

The troll rush event!! Being a priest on that boss/event is just so much FUN. Throw a heal here, run up to another as fast as you can, heal him, throw some pains here and there. All in all, a very fun fight.

Ok. Over to lvl 60 instances.

I really like the Rend encounter. Then again, I like the whole UBRS instance. I did it alot to farm the dragonrider boots, so I have alot of stories from that place. I mean, General Drakkisath is awesome as well. When the instance was new and hard, it really forced PUGs to start working with strategies. As a guy who pugged alot, I think its a great encounter.

I love Onyxia of course. It was my first raiding love. A big nostalgia bomb as well as a lovely fight. She had three phases, and the raiding-group really had to co-operate with eachother. The encounter required timing, vigilance, placement and you didn't have to equip epics to do it. It was at that time you could farm for blues for raiding, so you could really fine tune your gear, by farming 5-man instance. Also, this was the first time I experienced the fun of a guild, howlilg and shouting and talking on Ventrilo. The roaring form the commanders, and the MASSIVE howling when the beast died.

Baron Geddon! Hehe. Just gotta love that bomb gimmick of his. All the commotion that caused. I love this fight just because of how he could stir up a fight on Vent.

I love Ragnaros of course as well. The most epic time I have ever experienced in any game is when we downed him. (And how we shouted when we downed him :P ) The encounter was so great. As a combination of Shadow Priest and healer (yeah, I was one of those), it required me to run around alot.

Oh and last from my oldies list, is Razorgore. Remember how uptil then most fights always had gimmicks, but really wheren't that advanced? To wonder it took so long for guilds to down this bastard. This was the first taste of an encounter where you really had to run around and be on your toes, and be creative with your strategies. And as a Shadow Priest/Healer, it was so much fun, as I had to heal people all the while slowing down mobs that passed me with Mind Flay, as to help the guys that kited them.

After that and a few attempts at Vaelstrasz, I had to quit because my school started demanding alot of time. When I hear how much fun my friends had at the other bosses later on, I feel kinda sad. Oh well, was still alot of fun though.

So that's my list of most favourite encounters (though in reality I could've added ALOT more). Was fun venting the nostalgia.

Onyxia by far. Epic battle, even for 5 80's.

HOGGER ofc no contest!