I went to DC and Baltimore a few weeks ago. It was pretty neat. I'd been to DC a few times before so I went and saw the buildings I'd never seen before. Mainly the Department of Justice, the EPA and the Library of Congress. If you want to tour the Capitol building you need to get tickets in advance. You can get them online or write to your representative, they are free. Same for the Whitehouse, but you need a group of at least 10 people I think. The Spy Museum is good. The East Building of the National Gallery of Art was designed by I. M. Pei and has an absolutely amazing tunnel going between it and the other half of the museum. The walls are covered in millions of LEDs that light up in really cool patterns. Union Station is where most of the tours start, there's one tour on both land and water using an amphibious vehicle.
The aquarium at Baltimore Harbor cost $25 so I was stuck looking at the huge atrium with a rainforest growing inside from the outside.
I ate at a place called Nick's on Cross Market Street. I paid $13 for a soft shell crab sandwich. It was pretty good. The alternative was to eat at one of the seafood restaurants in the mall which cost significantly more (about as much as a ticket to see the aquarium).