Jet Blue Airlines is offering an All You Can Fly Monthly Pass for $599 according to their website.
"Enjoy unlimited travel with our All-You-Can-Jet Pass! For just $599* you can take JetBlue anywhere you like, as often as you like, from September 8 to October 8, 2009. Use your All-You-Can-Jet Pass for business, for pleasure, to visit your favorite cities or to meet with a client. You might as well just do it all! With more than 50 cities to choose from, and for just $599, it's a deal you can't pass up."