I find it interesting that only a few airlines (as far as I know) have regular low-fare programs in place, as opposed to occasional sales on certain flights. The brilliance of this concept is understated--restrict travel to a certain few days when traffic is at its lowest, sell fares for low prices on those days, and fly full aircraft instead of leaving seats open.
Comair, the Delta Connection affiliate out of Cincinnati and Orlando, offers a Weekend Travel Program, which allows you to buy a four-coupon booklet for travel at any time on any flight on Saturday, Sunday, or before noon on Monday. It costs $321, and you have to use one coupon per flight, but if I lived in, say, Cincinnati, and I wanted to fly to Disney World for the week, I could buy the booklet and get there for just $160 R/T, including taxes. And I'd still have two coupons left over for another trip! Problem is, it's not a good deal for anyone who lives away from the Comair hubs or focus cities, because you'd have to use the whole coupon book to go on a trip, but what can you do?
Another interesting program is AirTran's X-Fares, which allows anyone between the ages of 18 and 22 to fly standby for just $47 a segment. The program is more than a bit condescending, especially in the way they market it, but you can't beat that kind of deal. Problem, again, is that if you don't live in Atlanta (AirTran's hub), you'll probably end up paying more to fly standby than you'd pay to go with a restricted reservation (if you're savvy).
Does anyone know of any other airline low-fare programs?