Bo Ryan would also be good, but i don't see him leaving Wisconsin for OU. This is not to say Wisconsin is a better program but with everything that is going on why would you make this step, whoever comes in will have some massive rebuilding to do, and if Capel stays he has the job of the rebuilding.
If OU could get Dave Rose to leave Provo, he would be an outstanding hire. Would run a squeaky clean program with a fun to watch up-tempo offense. And his teams are always extremely prepared. But, I don't think he's going to leave BYU.
As disturbing as it sounds to me, I think Scott Sutton would be a good hire. Young, passionate guy that coaches the hard-nosed man-to-man defense Sooner fans like to see.
Billy G. would be my first choice, but you would need to hire a babysitter to be with him 24/7. He would have OU back on top really fast - regardless of his "issues", IMO.
Tubby is a possibility. He wants a practice facility and is still waiting for one. He would have left for GA Tech if that opened. Does say he doesn't want to rebuild though....