Twitter:
You may want to follow the hashtag #ChannelBiz it is used by many people and as always some use it to promote their stuff but it is a lot of good information
LinkedIn:
There are a few really active LinkedIn Groups about channels:
Channels Of The Future
http://www.linkedin.com/groups?gid=1768647
Channel Excellence
http://www.linkedin.com/groups?gid=2698760
VAR Talk
http://www.linkedin.com/groups?gid=1246227
FaceBook:
I guess it is by far the most important source for business people to get to know their clients, partners, vendors... Those who think neee Facebook is personal and LinkedIn is business - think of it this way:
You want to be *social* check me out on Facebook. You want to be stiff and check what I did two years ago - ....
SlideShare:
A very powerful tool to learn and educate others
Check out Social Media Presentation No. 200,000 you'll love it.
Not really politically correct language though !!!
http://www.slideshare.net/XeeSM/social-media-presentation-200000