Originally Posted by boltor
US Airways has a flight from DCA to IAD via RDU for a little over $200 round trip. You can earn some miles along the way.
United has one with a stop in Montreal.
You can often also book a connection via Chicago between any of the DC-area airports on UA. I actually priced one out when I needed to be at BWI for a flight and needed some additional WAS departures/arrivals for a UA promo: DCA-ORD-BWI for something like $150 back in April.
Seems the loooong way around, though