Phil Gordon's Little Green Book

By complete coincidence, i just went to Vegas to play a concentrated amount of no limit with both the Gordon book and Ciaffone and Reuben. I think the two complement each other very well. Newer players will get a lot more ABC stuff from the Gordon book, while Ciaffone and Reuben has a lot more depth to it when you start thinking about the concepts they present. It depends on your experience and how much you want to be spoonfed, but for people that are relative no limit noobs like me starting with gordon and moving on seems like a good bet.