Some that happened during my play time(Started in 3.0.8):
-Ensidia Saronite Bombs
-Retlol bug in 4.3 with Seals
-ADDINATIONAL INSTANCES CANNOT BE LAUNCHED haunted me for many weeks, missed out on 2 BHs on my main during Cata
-Powershot has a -90% miss chance by default. I was testing this on my friend in duel, he was SITTING still and I did like 5 Powershots, none hit the target(no miss/dodge/parry or nothing)
-4.0.1 in ICC as a Warlock, Destruction was OP as fuck, then 4.0.3 nerfed Destruction by a flat 18% lol
-Mage soloing a Quarter of Naxx with the spellsteal-able shield from a mob
-Yogg Saron +0 exploit with Warlocks using Drain Soul to not gain any Insanity
-Vashj'ir quests bugged at Cata launch, so many got fucked trying to get Server Firsts xD
-Super Wand during MoP beta, casters doing super damage with it lol
-Instance Servers crashing at MoP launch, my dung team got in while like 3 other teams were locked to Loading Screen bug