As an Iowa fan I find it strange about your guys' fixation on rivals over here, and I know that so much of it has to do with your Big 8 past with Oklahoma. Since that is not there any more, you should embrace what is to come in the Big10. For a rivalry, think of it this way... If you lost every single game on the schedule except for one, who would you want to beat? Who would the players want to beat the most? That is your rival...
For me, as an Iowa fan, it has sort of changed depending on certain years. For instance, the excitement of Nebraska coming to the big 10 made me want to really beat you guys at first. Fleck being hired at Minnesota really makes me not like them at all. Then you have Wisconsin... they are the one's I probably hate the most right now because they have what we want. Plus, screw Iowa St. I tell myself that I would give anything to beat them when we play them, but the minute the game is over, it becomes an afterthought.
Either way, why get frustrated trying to figure out who your rival has to be?
Rivalries can be fluid, they can adapt with team goals, you can have more than one rivalry, in fact, in any given year if your "traditional" rival is playing at a much different level from you, that might not be that teams biggest rival that year, or at least on the team's biggest game.
Anyways, enjoy coming to these boards from time to time because your members can be all over the place on a lot of different topics, so I end up thinking outside the box over here.