If you like trading on margin, there are two short sells I would recommend:
Google and SkyWest. Any other publicly traded regional would be a good short. The finance guys at the majors are starting to figure out how to shop capacity, and as they become more efficient at it, I would expect the regionals to begin to really feel the pinch. There was even an article in the WSJ yesterday highlighting the fee for departure schemes that run the regional bottom lines are on the way out.