JetBlue is offering $50 off travel between September 5, 2007 and October 31, 2007 after you book a roundtrip by June 1 for travel commencing by June 15. Registration required.

Thanks to reader Sloan for the pointer.

Pair this with $10 off each way when buying your qualifying roundtrip. (Here’s the link via American Express.)

Purchases need to be made with an American Express card by May 31 for travel by June 13, and Friday and Sunday travel are excluded.

While the promo rules say the offer is good on transcontinental flights, that doesn’t appear to be true — the special fare comes up from Dulles to Orlando, for instance, and becomes as low as $39+tax one way.