I've been pretty bad about picking books up for the most part, since I'm obviously not made of money. I'm actually looking at getting a decent bonus check within the next couple of weeks as well, so this may become a reality for me.
There are still some older titles that I want to pick up:
MM II
FFG's Traps and Treachery (maybe both volumes)
AEG's monster book (I think they are the ones that recently put out a big monster book; I already have ToH, but the more the merrier)
Monkeygod's Black Ice Well module (gonna integrate it into the campaign I'm working on)
All I can think of off hand.