Great question.
My take:
1979 Ohio State. Undefeated and #1 going into the Rose Bowl.
2004 Oklahoma. As bad as they looked against SC, they were undefeated and #2.
1978 Alabama. They did win 1/2 of the national championship that year.
Others to consider:
1938 Duke and 1939 Tennessee. Both came to the Rose Bowl undefeated, untied, unscored upon, and ranked in the AP top 3. Both lost to SC.