Mashable.com is leading the call for social awareness and charitable giving with the Summer of Social Good initiative sponsored by Zappos.com and MailChimp.com and benefiting four charities: The Humane Society of the United States, Oxfam America, WWF, and Livestrong - The Lance Armstrong Foundation.This week, Mashable.com issued a challenge to all participants in social media asking them to donate $20 and/or help spread the word about the Summer of Social Good in an effort to raise $100,000 for the four charities during week 1 of the Summer of Social Good campaign (which runs from June 1 - August 28, 2009). You can read all the details on this post on Mashable.com, which also includes details about tweeting and links for donating.