The current non-mainstream stuff I'm listening to right now is:
DJ Shadow - everything from "endtroducing" to some rarities
Apocalyptica - if you like metallica, a lot, and you also like classical music, this is really worth a listen
USS (Ubiquitous Synergy Seeker) - a band out of Toronto, they're self described as "Buddy Holly playing at a campfire in the middle of a drum n' bass rave at the Science Center. Bob Marley in a Lab coat. DJ Premier walks in." My fave tracks so far are "2 and 15/16ths", "Porno Star Trek", "Hollow Point Sniper Hyperbole."
Those three songs are available to play (not download) at
http://www.myspace.com/ubiquitoussynergyseeker