For the month of February US Airways is offering 1,000 bonus Dividend Miles per Shuttle flight. This includes all nonstop flights between Washington (DCA), New York (LGA), and Boston (BOS). These segments can be part of a larger itinerary and still qualify, as long as you have nonstop travel between those cities as part of the itinerary.
Registration is required using promotion code SH1K prior to travel, though there don’t appear to be any restriction as to when travel has to be booked (in other words, previously booked itineraries seem to qualify).
Bonus miles should post within two weeks of travel.
(Tip of the hat to The Points Guy)