I second rdales recommendation for Harrington on holdem... also read Poker and the Art of War, and that was very entertaining, if not as informative as Harrington...

For NL cash games I think the book by Ciaffone (don't know the title) is the best one out there. But I've never read it so take that for what it's worth.

I was checking Ciaffone in Amazon and there are two books by him, "Improve your Poker" and Pot Limit and No Limit Holdem"

Which one would be....??

The pot-limit/no-limit one is great for NL cash games. I read the holdem section probably 6-7 times when I was first starting out.

Improve your poker is a great book also, I would say it is for limit not NL, although it has some great poker concepts.

I have now read a couple of poker books, and I can't say I've read anything really relevant that don't already exist on various poker sites. Some guys on the net write better articles and more hands-on stuff then these authors do.

Ciaffone: PL and NL Hold'em (good but mainly for higher limits)
Cloutier and McEvoy: No-limit & Pot-limit Hold'em (geared towards tournaments but also good for cash game)
David Sklansky: The theory of poker (must read)
Larry W. Phillips: Zen and the art of poker (not a strategi book but I think it's the book that has improved my game the most)

There are other good books but these are what I can think of right now. But still I think you will learn more if you read 50 post on this forum, than you will learn if you read one poker book.

For people starting out in NL I would suggest reading Cloutier's NL/PL Hold em first... Then move on to either Ciaffone/Reuben's NL/PL book which is great or Super System 2, either way get them both read. Those are the best 3 NL books out there.