Jonathan Coulton is a singer/songwriter who is best known for his songs Code Monkey, Re: Your Brains, the ending theme (titled "Still Alive") to the video game Portal, and his light acoustical remix of Baby Got Back. He's remarkable in that he has released his songs free of DRM and with the Creative Commons license (the attribution, noncommercial, 3.0 version). For one year, he strived to do one song a week under his Thing a Week project.
Since so much of his work has been released under the Creative Commons License, the first exposure that most people have to his work are videos which use his music as a soundtrack. There has been machinima made featuring WoW characters to the songs of Re: Your Brains, Skullcrusher Mountain, and Code Monkey. In addition, Code Monkey is now being used as a theme song to the show with the same name on G4 television.
Much of his songs are available to be both listened to online as well as downloaded from:
http://jonathancoulton.com/