In addition to the above links, http://www.webmonkey.com/ is very good too. I learned most of my web skills from them. Stylesheet tutorials are <a href="http://www.webmonkey.com/webmonkey/authoring/stylesheets/">here</a> and <a href="http://www.webmonkey.com/webmonkey/authoring/stylesheets/tutorials/tutorial1.html">this</a> is a great beginner stylesheet tutorial.

With all of the quality links in this thread, if you don't become a stylesheets expert we're all going to beat you with wet socks.