All of my first choices have been posted:
Michael Jenkins, "Holy Buckeye"
Will Allen INT vs TSUN 2002
Cie Grant off the edge
Eddie vs Illinois, "Hello Heisman"
I'd have to go with the long TDs against Notre Dame in the Fiesta Bowl. More specifically, the two TDs by Ginn--even more specifically, the pass he caught for the first OSU score of the game.
After hearing so much for a month straight about the "offensive genius" Charlie Weis, and getting so much crap from Token Notre Dame Fan (the guy who was born and raised in Ohio but for some reason hates OSU and loves ND, I'm sure you all know one of these people), I was very anxious for this game. ND took the ball down the field and scored instantly, and for a second there was that "oh crap" feeling. Then the Bucks answered instantly... I remember watching Troy throw a deep pass downfield, the camera hadn't yet panned out far enough to even include Teddy in the shot, and I remember just thinking to myself, "Be there.... be there..."
Camera shifts to Ginn, 15 yards past the defenders, catching it in stride. Goosebumps every time.