By now, you've hopefully had a chance to look through all the Achievements that we'll be seeing in the Achievement system to be released with WotLK. There's definitely a lot of them, and they seem to cover almost every possible angle of the game. Still, there's bound to be one or two good ones Blizzard missed.
In this Beta forums thread, which is apparently being watched by Tigole, people have begun offering some pretty good suggestions for possible achievements that could be implemented in the future. Gish of Lich King suggests that one could get achievements for collecting full tier armor sets. Pez of Lich King suggests class specific achievements such as number of Mage tables summoned or number of lock boxes picked.
I'd like to hear your suggestions too. Is there an Achievement that you'd like to see in Wrath of the Lich King?