Lots of great information on that site Dominique mentioned, particularly in the forums.
One way to stay ahead, or at least to recognize tricks being played on your sites, is to read the blackhat sites. :crazy:
An extremely interesting article at syndk8.com, is a white-hat vs. black-hat debate between Earl Grey, professional Search engine spammer (and operator of the Black Hat Syndk8 forums), and randfish, well known professional white-hat SEO:
xhttp://www.syndk8.com/interview_with_a_black_hat_seo.php