A small list of most important webdev-related sites for me:
www.php.net
www.mysql.com
www.csszengarden.com
www.sitepoint.com forum tips
www.webmasterworld.com forum
www.hotscript.com scripts
www.dynamicdrive.com dhtml, java scripts
http://commons.wikipedia.org
www.drupal.org
www.joomla.com
google code search