Can't quite believe that I hadn't heard of Jonathan Coulton until recently, but now I have I can't stop listening to him. Funny, geeky, talented and well worth checking out.
Here's his official site where you can try his music for free. But if you like it, please pay the man. I recommend "Tom Cruise Crazy", "Re: Your Brains", "The Future Soon" and "That Spells DNA" (DM me if you want more recommendations).
And here is a handy video of "Tom Cruise Crazy":
Wish I could go on about this, but I'm super busy. Sorry.