Learning XHTML, CSS, and PHP

I am always setting goals and writing lists, and one of my goals is to teach myself XHTML, CSS, and PHP. I'm doing this via books and online reading in my spare time and evening hours. For those of you who might be interested in these subjects, I found some great sites for reference, interesting reads, and general nerding out.

http://alistapart.com/

http://www.webstandards.org/

http://www.google.com/dirhp (good for research)