1) "Glory of the Hero" when it was current, it was also one of the things that got me hooked on achie hunting
2) "What a long strange trip it's been!" took me 2 years, because i missed some of the events, and some i couldn't finish in year 1 because of IRL stuff.
3) Loremaster. I might have finished it in cata, and it took me 2 years aswell, because i rarely was in the mood for it, and if i tried to force myself i would quickly get bored and alt+tab and AFK out of the game...
4) (soon) Insane in the membrane. Started 3 years ago (same reason as Loremaster) and i'm halfway done with Ravenholt now. Leveled a rogue to farm lockboxes when time came, moved server, leveled new rogue to 62, got bored with the leveling, boosted it, and now i'm farming on it