I grew up in D.C. so you are in for a great vacation! There are so many things to do and see in D.C. One of the best parts of visiting DC is that the National attractions (e.g., the Mall (the area where most of the muesems are located), Zoo, White House Tours, etc.) are FREE. Restaurants are fit for foodies, but be fore warned that the food tax is 10%, so with tip expect to add 30% to the cost of a meal. The Hayadams is great, but pricey (I've stayed there and didn't think it was worth the dime (great service though)). Definitly stop by for a happy hour drink or two, if you want be check out the polical power scene. National is a great airport and is connected to the Metro, so you don't really need a car to get around. There is just too much to DC to outline in one post, so I'll pop in and add more comments as your trip gets closer.
P.S. Boo to Icehog's Mayor Berry comment! IL politicians don’t necessarily have the greatest track records either…