I tried Hammerhead but it's for loops, not the best thing to build tracks, but it's free.

Here's a link for music freewares

http://www.musicware.dial.pipex.com/


You can also surf in this page

http://www.synthzone.com/drums.htm


This is a link page for loops, can be useful

http://www.entropymusic.com/freeloops.htm


Fruity loop is good but it's not free