Here in Tampa, we have a magazine of sorts called The Advisor (I believe its a college magazine) and every other page has a listing of where pre-screening passes will be given out.
Also, my local Tampa Tribune newspaper gives tickets out at there downtown office ALMOST every day. Scored some pre-screening for Shaun Of The Dead, Gothika, The Forgotten and most recently Cursed (thank GOD that was free) and Hostage starring Bruce Willis (which doesn't start til next week.
In fact they gave away pre-screeners for Robots today, but they gave 'em away at 5pm and traffic in downtown is HELL so I'd rather pass. I wanna see it in IMAX anyway.
Bottom line advice: Check your local newspapers & local college mags!