We got into DC around 2:00 and checked into our hotel. It was rainy and our hotel was initially a little hard to find. The Residence Inn by Marriott is a very nice hotel; we had a 2 bedroom suite with a small kitchen. The hotel served a complimentary hot buffet breakfast every day. It also served a complimentary supper on Monday - Wednesday evenings. It was located in a pretty convenient place very near a metro stop and within walking distance of the capitol. It also had a couple of computers that guests could use to access the Internet, which was handy.
Once we unpacked, we took the metro to Smithsonian station and viewed all the major memorials. We checked out the Washington Monument (decided not to actually go inside as a one of us doesn't care for heights). We walked on to check out the WWII Memorial (very nice), then by the reflecting pool and to the Lincoln Memorial (very impressive). We then checked out the Vietnam Wall (sobering) and the Korean Memorial (creepy). We walked on over to the FDR Memorial (large and nice), then finished up our memorial tour with the Jefferson Memorial (also nice).
Lots of walking for our first afternoon; exhausted, we took the metro back to the hotel, walked to McDonald's for supper, and took advantage of the pool and hot tub at the hotel.
I was surprised at how easy it was to fit them all into a single afternoon; again, lots of walking, but very do-able.