Concorde
The best special was a couple of years ago when you could get Starwood (?) points with Inside Flyer subscriptions, which could be changed to Qantas miles which in turn could be used to buy British Air tickets on the Concorde. Folks hereabouts went crazy, and quite a few took their first (and last) round-trip flights on the "Speedbird" at a cost of only about $1250.