When I was in Washington last month, I needed a few hours of wireless access, and ended up at Panera in Chevy Chase (just across the Maryland line). If you're in Northwest, this could be an option for you. I was there from about 2 pm - 5 pm, had a sandwich and a bottomless soda and easy access to an outlet. They weren't at all busy then, so I didn't feel too bad about taking up a table for three hours.