1. Throw the works at him and Make Urban Meyer tell ya no.
2. If Urbs is a no go then go for Paul Chryst. He'd bring Nebraska it's identity back of tough guy running and defense. The guy has a good record in the BIG and is a two time coach of the year in that conference. Wisconsin screwed up letting him go so take advantage of their mistake, solid/safe choice in this situation to get NU back to at least some respectability.
3. Matt Campbell, He should have left Ames already, he has taken them about as far as he can and has done a great job building their program, IMHO he'd be a terror at Nebraska.
4. Dan Mullen, Urban Meyer coaching tree, Florida was a mess but it has been for a few different coaches. He did a solid job at MSU which aint the easiest place to have success. Nebraska needs to run the ball, Mullen can make that happen.
Past that, total crapshoot so take my advice, get one of these guys.