Tennessee could be another good one for Wisconsin. It's within driving distance (sort of), it's recent history has made it, perhaps, more likely that it would sign up for home-and-homes with Wisconsin. It's got a cool stadium in a great location. And it's a program that should be on the rise back to some semblance of its former self.
I would, of course, love a series with Notre Dame, but it's not all that interesting from an away game perspective. Another trip in the Midwest near Chicago? Meh. It's not as though South Bend is the end-all-be-all of college towns. Notre Dame has a gorgeous campus, but for alumni there isn't much about South Bend that's attractive as a destination (as opposed to Raleigh, Berkeley, Pasadena, Seattle, Austin, Knoxville, or Atlanta/Athens).