National Museum of Health and Medicine

A smaller and out of the way museum in Washington DC area, if you are interested at all in Medicine, this is worth the trip. This use to be located at the Walter Reed Hospital area but now is located in a stand alone area. Artifacts from the US military medical corp through history can be seen here. A really interesting display relating to the assassination of President Lincoln, including the actual bullet, is displayed here.
link to their website – medicalmuseum.health.mil