The name's I've heard most frequntly when Heisman talk comes up are Florida's Tim Tebow and Percy Harvin, The Ohio State University's Chris Wells, Oklahoma's Sam Bradford, Missouri's Chase Daniels, and my personal favourite, Knowshon Moreno of Georgia.
Personally, I think that Georgia's been out of the big picture for too long. Knowshon Moreno caps off a 1 loss season and a #1 BCS ranking with a Heisman win. I wouldn't be surprised if Moreno's teammate Matthew Stafford joined him in the final five.
One thing you can be sure of is Tebow will not repeat.