http://www.facebook.com/ (really? If you aren't on Facebook yet, we need to talk!)
http://www.instagram.com/ http://www.meetup.com/ http://www.twitter.com/
Bonus points: Logon to to http://mashable.com/smday/ to see if there is a Meetup scheduled in your hometown. You are sure to meet a ton of people and learn. Strange enough, here in LA, our Meetup currently has no details! But social media lovers are biting at the opportunity. If deets aren't up soon, this is going to be a crowd sourced event!!!