Social Network:

http://www.boonex.com/products/dolphin/doldemo/ - Complete Web 2.0
Social network software. Fully Ajax system with tons of features! This
is the mother of all socialnetwork software. And best of all its free!

http://www.pligg.com/ - A great DIGG like CMS system build with AJAX
and great SEO system.

Tools:

http://www.iwebtool.com/tools/ - A collection of great online tools
every webmaster could use from time to time. Check it out

CMS:

http://modxcms.com/ - Ajax CMS system with SEO urls!
http://info.tikiwiki.org/tiki-index.php - Tikiwiki is a HUGE CMS
system with a tons of featuers like, wiki, forum, blog, digg, dmoz.
http://jaws-project.com/ - Pretty neat and upcomming AJAX CMS system
http://www.xoops.org/ - Another great CMS system and Framework


Images/Icons:

http://www.iconarchive.com/ - Million of nice pictures and icon for you to use for free

Scripts:

http://ajaxrain.com - Small but very nice and handy scripts to spice up your website.