It would be a joke not to vote Tim Tebow.  Even though I'm not a Gator fan, it's obvious that he has been consistantly spectacular all season long.   He has a combined 51 total TD's this season and is elevaing the QB position to another level.  He is taking what Mike Vick and Vince Young did in the NCAA and improving on it.  He is definitely the most outstanding player of the season.  If he has a similar season next year, he should go down as one of the top 5 players in NCAA history (that would give him career numbers of 63 TD passes, 52 rushing TD's, and only 13 INT's. . .WOW!).

For me it comes down to two players. 
Hawaii's Colt Brennan and Arkansas' Darren McFadden. 
They both change the complexion of the game when on the field.  That is what great players do. McFadden had LSU worried everytime he was on the field.  Brennan the same with BSU.
The Heisman is for the best player in college football, and that gets lost among the voters and fans some years. It is not an award for the most valuable to his team, nor who will make the best pro or will be drafted the highest. 
Brennan has a very strong arm, can move if he has to and can find his targets even as teams make adjustments. He can throw it short, he can throw it medium and can go deep.  He is accurate and can throw across the field with strength.
McFadden seems to have the ability to play it anyway you need him to.  He can run tough, he has speed to get around the corner and then he has an extra gear that fools defenders that think they have an angle on him.
The tie breaker for me is the fact that Brennan handles the ball on every offensive play.  He gets my vote.