Links
SharkScope: Find out the tournament history of your opponents. This is great for getting some kind of feel for opponents you've never seen before. Also, you can apply to have your stats removed so people can't look you up. Unfortunately you can't see their ring-game stats, and the amount of searches per day is limited unless you feel like paying for it.
Harrington on Hold'em: This book will take you from a beginner to a well above average no-limit Texas Hold'em player. Honestly, I've never read another Hold'em book that I really thought was worth anything. Covers pretty much all the important subjects in an easy to understand way with lots of examples, while managing to incorporate subtle important winning concepts. A must-read for the aspiring online star.
SuperSystem: While seriously dated (it was originally published in 1979) this book is a classic. The major flaw is that antes are included in hold'em where they don't exist today. The reason to get this book is the great explanations of other games (I personally found it very helpful in clearing up my misconceptions about 7-card stud). If you just want to learn online no-limit Texas Hold'em, then this probably isn't the book for you. If you want to learn how to play many of the other major games still played today and also some really interesting poker history, then it's definitely worth a read.
