I think MSU is the most memorable for a few reasons.
It was the first time Iowa EVER went 8-0. It was the only the SECOND time in Big Ten history that a team has won @Penn State, @Michigan State, and @Wisconsin. It was the first time under Iowa for Kirk Ferentz to win in East Lansing. It was the hardest hitting college football game I've ever seen. Iowa got its highest BCS ranking after the game EVER. It culminated in two of the most dramatic offensive drives ever in Big Ten history. It was the macrocosm in micro. It ended on the fourth most exciting Hawkeye play I've ever seen: #1 was "The Kick" by Rob Houghtlin, #2 was "The Catch" by Halloway, #3 was "The Kick Part 2" vs. Penn State last year, and #4 was what I am calling "The Slant."
For the most infamous victory, I would vote "The Blocks" vs. UNI