Things to see in DC

I will be in Quantico, Virginia, for the Boyd conference Thursday and Friday nights, but starting on Tuesday I will be in Washington, DC itself. The following sites have already been suggested to me:

International Spy Museum
8 and F Streets NW
Right by Gallery Place/Chinatown Metro Stop (Yellow line right from
airport, also Red and Green)

US Botanic Gardens
245 1st St SW (just off the southwest corner of the US Capitol grounds)
Either Federal Center Southwest or Capitol South Metro Stop (Blue Lines)

US Holocaust Memorial
Right along Independence Ave and 14th Street
Smithsonian Metro Stop (Blue/Orange Lines)

Biggest Church in America
Brookland-CUA Metro Stop (Red Line)
Take the CUA exit out

Arlington Cemetery
Arlington Cemetery Blue Line Stop

What else is worth seeing in our nation’s capital?