Non-profit HeadCount.org Rallies over 200 Musicians, Actors and Comedians to Support "National Voter Registration Day"The largest social media-driven voter registration campaign ever was unleashed today by the non-partisan organization HeadCount, to mark the inaugural National Voter Registration Day. More than 200 celebrities and musicians from 50 Cent to George Lopez to Dave Matthews took photos holding up HeadCount's "Register To Vote" clipboards. They are sharing their photos on Twitter and Facebook today, along with a link to an online voter registration form.Register to vote HERE!The musicians, actors, and comics featured in the campaign have a combined social-media reach of over 100 million followers. Other participants include Stephen Colbert, John Legend, Sarah Silverman, Jack Johnson, and Edward Norton. Dave Matthews Band also released a special video for their new single Mercy that links to the online voter registration form and ends with Matthews writing "Register to Vote" on a writing pad.