This isn't the first time an airline has offered such a perk, but it's noteworthy: for travel between Sept 1 and February 29, 2008, American will require 15,000 frequent flyer miles instead of the usual 25,000 for travel up to 750 miles in length.

That means you can fly from Dallas to Denver, Chicago to Atlanta, Philadelphia to Chicago, or St. Louis to Dallas, for example, for just 15000 advantage miles. American says this
"sale" will be available for a limited time, but they don't specify an end date.