Very interesting to see everyone's opinion on this matter. I agree wholeheartedly that Washington DC is a must stop for any visitor. One of my favorite places to visit myself. There is just one cool and interesting piece of American history after another in that city. Don't miss the Great Lakes either, I grew up in Michigan so I am a bit biased but they are amazing, especially Lake Superior and Michigan's Upper Peninsula. They are an often over looked destination by many tourist European as well as American.