A nice set of freebies, but might be a bit below your level. Nice to know about to pass to ppl as an intro!

http://mybroadband.co.za/news/genera...rce-books.html

For a more advanced level for nix then I recommend the LPIC study guide as an err guide!

http://www.happy-monkey.net/LPI/

Lots of great tip websites such as:

http://www.linuxcookbook.com/

http://www.thegeekstuff.com/

http://tips4linux.com/ {kinda slowed down }

and ofc how can we forget.....

http://www.linux.com/