Having visited a number of cities in the US, I have to say I agree with Washington DC here - I found it to have the most touristy things to do, be a great place for exploring on foot and home to good bars and restaurants.  Not a place many people from across the pond have as their first choice (usually NYC, Vegas, San Francisco or LA) but my favourite city of the lot.  And seeing all the monuments lit up at night is just amazing.