Aw, you'll be in DC now that I'm not! Have a great time. I highly recommend the museums of Air & Space, and Natural History (my favorites as a child).
Can you recommend any anime stores or restaurants?
Alas, DC is (surprisingly) not very good for Japanese stuff, unlike Boston or NYC (or, I suppose, Chicago). There are no Japanese bookstores at all, for instance, and I can't think of any place to buy anime-type stuff that isn't a national chain.
There are plenty of good restaurants, but I'm severely out of the loop after not having lived there for so long. My sister did introduce me to a good Ethiopian place this last time, though -- Zed's, in Georgetown. If you go, get the honey wine, even if they tell you it's only for dessert. ^_^