I'll second Otto Graham. In a 10-season career, he played in 10 AAFC and NFL championship games, and he won 7 of them.
<img src="http://www.footballcardgallery.com/pics/1946-Sears-Browns/5_Otto_Graham_football_card.jpg" />
<img src="http://www.footballcardgallery.com/pics/1946-Sears-Browns/5_Otto_Graham_football_card.jpg" />