This is not a complete list but it's a great start.
Ping.fm - http://www.ping.fm/
Allows you to post to all of your networks from one area.
The service is Free and Essential.
Retaggr.com - http://www.retaggr.com/
Create links and interact with multple social media networks. You can also create a profile that links to all of your SM profiles.
SocialMedian.com - http://www.socialmedian.com/
This is a great source of news for all aspects of social media.
CrunchBase.com - http://www.crunchbase.com/
Provides extensive data on social media companies.
Go2web20.net - www.go2web20.net
A very complete listing of just about every social media and web 2.0. Searchable by date, tag and name.
Flock Browser - www.flock.com
Flock is Firefox based browser designed for social media. It is a must have if you have multiple social accounts, blog, twitter or basically do anything social.