This is of course destined for warlocks only. Lots of us maybe know that, but I bet, there are people who didn't even saw Warlocks Den. This guide, reffering to gearing warlock on all levels and especially end-game, wasn't written by me, but it's so good, that I've had to post it here:
Gearing Your Warlock (2.4 Edition) - The Warlocks Den Forums
(It's linked, because it's long)