First off, check out iFloyd the "spring sampler" Mix Tape for 2006. You can stream the whole thing online. Like what you hear? Download the whole thing in a zip file (link on the page).
The mix tape offers some damn fine artists, like punk supergroup and cover band Me First and the Gimme Gimmes doing a cover of '(Ghost) Riders in the Sky,' NOFX with 'The Man I Killed,' Against Me! performing 'Pints of Guinness Make You Strong' live; Love Equals Death contributes 'When We Fall;' and so on. In short, 14 tracks of awesome that samples some bands that are familiar to me, and quite a few that aren't.
Once you download the iFloyd Mix Tape, check out the massive MP3 download page sampling every band on the Fat Wreck Chords label. Oh, hell, do I spy with my little eye Anti-Flag?
I'll hunched over the downloads page until further notice.