DCA/BWI/IAD isn't bad depending on where you live. I commuted by metro for over 8 years to DCA. Only issue is the train closes at midnight during the week and doesn't open until 5am. Otherwise you are mostly covered for mass transit.

MARC train connects you between BWI and the DC metro for only $6. IAD will soon have a metro that goes all the way to downtown. But for now you can get there by bus or Marc train.