Definitely HOH is your best bet, as others have said. But there will soon be a book that will presumably rock the NL world: Ed Miller and David Sklansky's "No-Limit Hold'Em: Theory and Practice." This is promised for May 2006, but there is now a brief excerpt in the 2+2 online magazine (on the 2+2 site, obviously). I'm no expert on NL (I play mostly limit), but it looks mighty tasty...
The question is: will they make a giant thread on 2+2 questioning the credibility of other NL authors?! Gee, golly, I hope so!!!