As we recently mentioned, airlines want you to book on their Web sites, not with Kayak or Travelocity or Orbitz.
So they're offering promo codes. We just received this in our email, and perhaps you did too:
We're not quite sure if the discount code/certificate number works only for one time use (although it does say you can forward the discount to a friend). So sign up for the airlines' newsletters and save money.