To Morogrim, let's just say: an interesting encounter, and possibly the first time many guilds used a paladin to tank (albeit a holy one, for many). For that, we almost forgive the gratuitous murlocs. Karathress, a fun exercise in self-preservation as well as tanking and healing, was too reminiscent of Maulgar to let us ever really enjoy the fight. Leotheras, an amusing encounter simply because the concept of "get out of the way" was advanced raiding, was definitely a satisfying kill, though seeing tanks chasing after the boss often called for a Benny Hill soundtrack.
And Vashj. The complex positioning for elemental killing, the concept of looting and throwing cores, the add tanking and kiting, the joy of static charge and roots, the deadly green goo. Ignoring the quickly-hotfixed group loot method, Vashj was hard: there was a lot for every individual raider to get their head around, and simply saying "stand here and kill this" wasn't enough. Chaos on vent whenever someone looted a core, especially when they threw it to a kiter; panic as elementals leaked through, or tainted elementals despawned. Yes, Vashj was oh-so-frustrating to learn, but equally satisfying when she finally died.
On to The Eye, where blood elves died in their legions before our mighty wrath. Al'ar, a sight to make fire mages' eyes sore, was a barrel of laughs (look, tanks, you're supposed to jump down for the Quill) but Loot Reaver more than made up for it. Then there was Solarian; nerfed from needing heavy arcane-resist soakers to simply requiring people to move out of the raid, there was always plenty of room for a comedy wipe or two -- plus, in the days before protection paladins featured in every raid setup, the adds phases were a lot of fun.
Once you had those three down, though, it was time for the nemesis of pretty much every tier 5 guild -- Kael'thas Sunstrider, in the days before he had a less-angry clone in Magisters' Terrace. No boss has caused as much pain, tears and broken keyboards as the Prince of Quel'Thalas did in his day. The encounter combined many challenging elements, such as running away from things, not standing too close to other things, stopping DPS at sensible moments, busting out as much AoE as possible, keeping threat against said AoE, dealing with potentially-fatal Pyroblasts, not dying from fall damage, and managing pesky Phoenixes. If you managed to kill Kael without a single raid member ever dying to Thaladred, you deserve a special achievement.
Thanks, Kael and Vashj, for allowing entrance to Mount Hyjal; if your raid group was on top of things, your first Kael kill meant you could dash off to the land of trash wave heaven, soon to be followed by a jaunt into Black Temple.
To Hyjal, thanks for introducing us to a newfound hate of trash. It was okay the first time, and bearable the second, but really -- all we can say is thank goodness it's eight waves, not the original twelve. Sadly, the Hyjal bosses aren't exactly memorable, except perhaps Azgalor, a fight where wipes were avoided due to sheer unwillingness to redo the trash. Then Archimonde, who definitely gets a special mention.
Archimonde helped us discover a lot of fun and exciting facts about our raid force, such as who liked to stand in fire, who *really* liked to stand in fire, and for whom standing in fire was, well, a new day job. Not to mention the inevitable inability of raid members to use their slow-fall Tears, leading to a cascade of deaths and the inevitable wipe. I'm not sure anyone ever liked Archi, but fighting him was always educational.