If you sign up for the JetBlue emails, you should receive discount emails on most Tuesdays (the promotion is usually for one-way fares for $49, mostly for travel in the vicinity of the West Coast). This seems to be a perpetual offering from JetBlue, not a one-time promotion. I am a seasoned traveler (flying at least several times a month), and, to my knowledge, the more conventional airlines (Delta and United among them) do NOT offer such discounts. Virgin tends to have monthly promotions, though I'm not sure you can receive email updates. Check their homepage for these offers. The same goes for Frontier, which offers amazing deals on its website. Finally, while Alaska doesn't seem to advertise its promotions via email, they consistently (again, not occasionally) have remarkably reasonable fares (especially between the West Coast and Hawaii). Happy traveling!