Lundquist+-+comprehensive+list

The Masai build their houses of cow dung and consider their work of herding cattle to be sacred. Fast forward technologically and you have

Sacred Cow Dung, a cool list of web 2.0 applications categorized by types:

http://www.sacredcowdung.com/archives/2006/03/all_things_web.html

A second site, categorizes and provides annotations when you hold your cursor over the site icon. Clicking on the icon brings you to a fuller description and links to the application's site.

http://www.go2web20.net

I found the wikipedia list to be the most interesting and useful overall:

[|http://en.wikipedia.org/wiki/List_of_social_networking_websites]