As many of you know, online Web zine Pitchforkmedia.com is the tastemaker of independant and underground music these days. They've put out a book, "The Pitchfork 500," which documents some of the greatest music made "From punk to the present." I've got a free copy of the book to give away. All you have to do is post a comment about a song that you think is one of the best in the last 30 years. I…