It seems like there's nothing the Internet can't do these days.
The website Crowdsound is the brainchild of programmer Brendon Ferris, where users are coming together to collectively write a song. Over 15,000 people have participated so far, and the song is currently working its way through its conclusion. Each note must be voted on by at least 50 people before it is finalized, so it'll still be awhile before the song is finished.
Once the melody is finalized, the next step for the project will be crowdsourcing lyrics. While Ferris hopes the song will be appealing to everyone due to its crowdsourced nature, it's hard to imagine a song with lyrics written by the anonymous crowds on the internet being ready for polite company. Maybe he should just stick to the melody.
In any case, voting is still open here, so make your choices wisely.