Just read on ESPN an announcement that the SEC and the Big12 have entered an agreement, effective in 2014, where the conference champions will play each other in a New Year's Day bowl for the next five years.
"A new January bowl tradition is born. This new game will provide a great matchup between the two most successful conferences in the BCS era. ” -- SEC commissioner Mike Slive
The exception to the two conference champions meeting would be the those qualifying for the final four/BCS playoff. In that case the next two most "deserving" would go.
I don't know how you decide most deserving other than the team which lost in the championship or whoever has the highest BCS rank after conference championship game. No details on that one, but the fact that there's an agreement is pretty funny as this takes a direct shot at the Rose Bowl's Pac50 and the other Big conference.