Mashable is the world's largest blog focused exclusively on social networks...
http://mashable.com

http://mashable.com/2006/08/23/widge...t-marketplace/
http://mashable.com/2006/09/14/thesp...space-widgets/
http://mashable.com/2006/08/02/we-lo...s-for-myspace/

And YAHOO!
http://widgets.yahoo.com/

Phil