Sonic Youth's Thurston Moore has started protest-records.com with MP3s of protest songs. You can also download Masters of War covered by Carla Bozulich of the Geraldine Fibbers from Cry by the Scott Amendola Band at cryptogramophone records.

There are only eight songs
so far on protest records including "New New New War War War" by Eugene Chadbourne, two Cat Powers tracks, and a song by Steven Taylor of the Fugs which inspired the project. You can also downoad stencils.

Chabib (Chris Habib) writes on the Sonic Youth board

new project that thurston and i are curating/building
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we literally just started it, but it's evolving everyday. we're sorting thu tons of links to create a refined list of alt/indy media outlets, activist groups, etc too. that should be up soon.

it's basically just a humble little archive of passionate voices that have been donated to us by artists attached to them. we have commitments for dozens of other tracks and i'll be making new stencils for that section of the site as events dictate they be created.

Update - Neils Strauss writes in the 3/26 NY Times:

Free Music

After 9/11 one of the first musicians to take on an activist role was Thurston Moore of Sonic Youth, the highly influential 22-year-old underground rock band. Mr. Moore began compiling little-known articles on world events, most with a liberal intellectual viewpoint, and distributing them to friends.

"I've always been a frustrated editor," he said.

Another one of Mr. Moore's longtime fantasies was to have a label that gave away music free. "I thought it would be great to be in a band that made millions of dollars that could do something like that, but it never panned out," Mr. Moore said, referring to earning millions. "I liked the idea because it would drive retail stores crazy. Originally the ideas were more far-fetched, like hiding the records around the city so that people had to find them."