Phil Gordon's Little Green Book

If you play Texas Hold 'Em, you should buy a copy of Phil Gordon's Little Green Book : Lessons and Teachings in No Limit Texas Hold'em. It's not a complete guide on how to play the game, but it's an excellent cookbook of recipes to improve your game. My favorite tidbit: the Rule of 4 and Rule of 2, which help you quickly calculate odds of hand improvement. Example: you've flopped an open-ended straight draw and want to know the odds of improving to a straight by the river. There are eight cards in the deck that could make your straight, so by the Rule of 4 you'd multiply 8x4 and conclude that your odds are approximately 32%. (They're actually about 34% but it's close enough to make a quick judgment whether pot odds justify a call.) Likewise, the Rule of 2 applies after the turn card. If you haven't made your straight draw by the turn, multiply that same 8 out cards by 2, and learn that your chances are about 16% of making it on the river. (Again, it's actually 17.4%, but it's close enough.)

Buy the Little Green Book today!