I've posted about Roadrunner Records before but I don't think I've ever posted a link to a facebook page as a means to acquiring free music before.
Roadrunner Records facebook page and "Like" them, you are taken to a page where, in exchange for your email address, you get to download an eight track sampler.
In the download you get tracks from DevilDriver, Revoker, Within Temptation, Cavalera Conspiracy, Times of Grace, Royal Republic, Underoath and the magnificent Black Stone Cherry. I am really impressed with the stuff the Roadrunner gives away. I assume they hope that once you have developed a taste for it by listening to the free stuff, you'll go and buy more from the artists you like. If that's what they hope... it works on me!