If you're just getting into security, or even if you've already been at it for a while, check out this site; it's got lots of great info:

http://www.sans.org/rr/

It's the best I've found so far. Tons of white papers categorized into 70 different sections.

If anyone else knows of other good sites for white papers let me know... I just can't get enough reading to quench my thirst for knowledge

IMO, white papers are the best and most reliable source for information about security.

Of course, another very good resource is the AO Security Tutorials Section. Take look at Negative's Tutorial Index to find tutorials on a specific topic.

Have fun

mjk