For me it was the 2004 de facto BIG championship game against Wisconsin. It finished in the cold dark night, and the place was going nuts. It was the 3rd consecutive 10 win season in Kirk's revival of the Hawks. Matt Roth went wild that night and must have sacked Wisconsin's shitty QB ten times. I recall Tate hitting Clinton Solomon after doing a spectular Houdini like escape in the pocket for a long TD. Place was unhinged.
I wasn't at the Iowa-Michigan legendary '86 game and also missed the epic OSU beatdown in 2017. Both of those were crazy from what I was told.