although I would caution that some certainly aren't 'social media' in the sense that most people would use it.
http://www.searchrank.com/blog/2011/03/ultimate-social-media-profile-chart.html
I'm pretty sure I have another list somewhere which includes some not on here - if anyone else has ones to add stick them in the thread with some details (category, countries, comments etc) and I'll try and throw them all in a single spreadsheet at some point.
This site is pretty useful:
http://targethut.com/
It has a somewhat realtime list of "target" sites to play with, primarily focuses on web 2 type stuff.
Data includes PR, pages indexed, backlinks and avg time to get your fresh page indexed.