Local pilots and planespotters will be happy to know that LiveATC has live streaming tower communications from National Airport (DCA) and Dulles (IAD). Few things are more soothing and fascinating for the aviation geek than listening to the smooth, seductive tower-and-aircraft dance of ATC broadcasts from your local airport.
You can also search for the pertinent airports from LiveATC search; National is KDCA and Dulles is KIAD. Found via DCTower.net.