During each day of November you can download a free track by the Grateful Dead during the "30 Days of Dead" celebration. The tracks are 320Kpbs MP3's and DRM-free. Tracks are from throughout their extensive career and usually lengthy (so far the shortest is 10 minutes and the longest is nearly 26 minutes).
You need to put an e-mail address in to download but just use a disposable one if you feel so inclined. Note that the e-mail address is required for each track but you can go back to previous days if you have missed any.
Only downside for me is the lack of ID3 tags in any of the files and the strange file naming convention but that's easily taken care of.
archive.org has alot of their tracks for free. i believe they uploaded the tracks themselves to the site.
http://www.archive.org/details/GratefulDead