i'd check craig's list - same applies to any major or moderate sized city. there are usually lots of rooms and sublets in DC. you don't want to have to rely on public transportation to get to either of those hospitals, in case they didn't tell you.... really GW and Howard are the only 2 that are metro accessible. i think Gtown has a shuttle from Ballston but don't know if it would do well w/ EM hours.
My med school has a program where students can be hosted by alums during away rotations/interviews. Perhaps your med school has something through the alum association?
As you may know by now, you'll do two weeks at each site. It's a good rotation, but admittedly getting to the sites is miserable without a car. On the flip side, for those few shifts you have that won't correlate with an operating shuttle, the taxi fare will probably still not outweigh the $6/day you'd be paying for parking. rotatingroom will be a good thing to look into. If you don't find anything in the next while, I can ask some of my classmates who are staying in DC that might have space. Good luck!
Your best bet would be to get a sturdy helmet and bicycle, and try and stay somewhere in between the two places (Columbia Heights, Dupont, U Street, Mount Pleasant, Adam's Morgan)
