Okay guys let's see how close you paid attention to the game last night because this answer was given right after the game. That is your hint, and please be honest no google search. Probably the only one I can trust on this is IMAPK.
Since 1950 there have been 4 Heisman Trophy winners who played for an undefeated National Champion. Mark Ingram did it last night, can you name the other 3?