"Crushing the Microstakes" by BlackRain79 is good, also "Dynamic Full Ring" by James "Splitsuit" Sweeney, I've heard good things about "Poker Math that Matters", and actually own it, but keep finding new stuff to read. Just picked up Matthew Janda's book. The first 2 you can pick up pretty cheap, but the other one is kinda new, but think i got it for $22.
This is a free e-book by the creator of Leakbuster that was up on the HM2 page. has some nice stuff in it. The sections on Blind play, 3/4 betting, and Perceived Range are really good. http://blogs.holdemmanager.com/free-nl-ebook-from-leakbuster-developers/