I'm also on Twitter (@millercallihan) and Facebook (though I only "friend" people I actually know personally or professionally), and I'm starting to use Google Plus a bit as well. Link is here; let me know if you'd like an invite and don't have one yet (whether I "know you" or not).
I use LinkedIn but have never found it particularly helpful in my line of work. A friend of mine gets head-hunted at least once a week via LinkedIn, though, so I think that one depends on your industry.
What other social media platforms do you use? Have you found anything else that's useful for self-promotion? What's the next big thing going to be?