I found this post from ReadWriteWeb that discusses how social media can be used for social change, including Jeremiah Owyang’s post about how to support the China Earthquate relief organizations and Facebook Causes (among others). That post highlights some great examples of how the forces of social media can be used for charity as well as networking with friends.
UPDATE: Here are a few other posts demonstrating how blogging can be used to as resources for the community:
Breast Cancer support like the topics covered by Why Mommy of Toddler Planet
Do you have any other links to share?