Any of the Blue Bloods obviously. UGA has only played OU once. Texas would be good, we owe them (and they owe us).
USC and ND would always come up in such a list. Penn State, Ohio State, Wisconsin, teams that line up and intend to try and mash you.
The most commonly played team of note is Clemson in history.
UNC would make my list for personal reasons, and the fact that both claim to be the oldest state university in the country.
And Eastern Michigan of course.