I've been to D.C, it's great - so much to see! Will you be at the Smithsonian at all? If you are in the capitol building, look carefully at your surroundings. Some of the hallways and floors have amazingly beautiful tilework. Will you be going to the National Zoo? Say hello to the pandas for me if you do!
http://nationalzoo.si.edu/

A cyclorama is a painting in a circle - do you mean the one at Gettysburg? That's a pretty famous one - see http://www.nps.gov/gett/gettcyclo.htm

What's the focus of your trip? History, or just sightseeing/political stuff? It'll be a very exciting time, be sure to take lots of pictures!

I have heard the Holocaust Museum is an extremely moving experience. Bring tissues.