The best book written on the subject of betting professional football. Period.

It is not often that that the honest and the articulate enter into the business of supplying the usually ungrateful and ignorant betting public with sharp and insightful information. JR Miller, a professional TV writer has done that with his seminal work on the topic, "How Professional Gamblers beat the Profootball Pointspread.

That being said, even if you never read the book, JR's website is chock full of nuggets of wisdom, that can also be applied to the other sports. Check out the following sections, print them out, read them and then read them again:
+ HOW TO SPOT SUCCESSFUL BETTORS
+ A CRASH COURSE IN VIGORISH, AND IT'S NOT 4.55%
+ Bob McCune on Betting Baseball
+ Kevin O'Neill on Different Games: College vs. Pro
+ Peter Ruchman on HOW LAS VEGAS SETS THE LINE

If there is one site that you do more than surf around on - this is it.