Kong is right although I have a few small critiques...
CU and Mizery are absolutely rivalries, or were rivalries. Colorado is more obvious but Mizery had a few upsets vs NU and there was a lot of hatred they had for us, and us them because of it. Also played a lot. I actually hate Mizery more than any other school including Texas. I hate their fans. I hate their team. I hate their mascot and colors, even though we beat them routinely. My father told me that it's literally in my blood, as my gpa hated them more than anyone, too. Mizery was actually pretty good a lot more than people realize.
One thing to note, however, is how NU fans tried to deny the colorado rivalry. Many NU fans tried to act like CU wasn't a rivalry, "only they cared about it", etc, which was not true. I always thought of them as a rivalry and hated them too but loved playing them. Most of the backlash was due to them replacing OU as the final game when the Big 12 happened. I feel as though we have a little of that with Iowa right now...a lot of fans don't want to call them a rivalry, but they really are the only rivalry we have now. It sucks, and it's a weak rivalry, and it's nowhere near OU, CU, or Mizery, but it's all we got. It doesn't feel the same because Iowa sucks so much and always has, and while they have had our number, it doesn't feel different than a loss to other teams because we aren't good. Hell we just beat them in what was perhaps the worst season in our existence last year. Weak. Big deal.
The best rivalry was OU. And it was respectful, although there was hate there, it was professional hatred between elite programs actually competing for something. The reason CU and MU fans throw bags of piss and bottles is because they aren't elite. OU was the best for sure. Our only hope of that again is conference realignment, ADs with balls in scheduling, or UCLA/Penn State on a yearly basis with our programs rising to top 10 status. Iowa won't ever be that, but could potentially be another Mizery.