I like music, but I like hilarious nerdy music more. Jonathan Coulton is a veritable factory of excellent nerdy music. Additionally, he loves us enough to let us sample all his songs on his website. Some of my favorites are even available for free download.
All of his music is released through the creative commons license, which has lead to many excellent derivative works, such as mash-ups and music videos. For those of you who have caught the karaoke bug (filk anyone?), there are karaoke tracks, with on-screen text, available for purchase.
So go check it out. You won't regret it.
My personal favorites are Re: Your Brains, Skullcrusher Mountain, The Future Soon, and (for those of you wearing headphones, this one's NSFW) First of May. Also, check out the video for flickr: