Here are the museums I’ve visited so far. Considering the sheer number of museums and monuments in DC, I’ve visited very few. It’s even less likely that I’ll get to them all.
Free Museums
American History Museum – A Smithsonian Institution museum. See a first ladies exhibit, the ruby slippers, and great rotating exhibits (Julia Child’s kitchen was on display the last time I visited).
Library of Congress – The Library of Congress is absolutely worth visiting and touring. The tours are free and docent-led. The paintings and sculptures are beautiful. If that’s not exciting, there’s also a Gutenberg Bible on display here.
National Postal Museum – A Smithsonian Institution museum located in the old post office museum near Union Station. The museum is dedicated to preserving postal service history.
Natural History Museum – A Smithsonian Institution museum. This museum is often crowded, but full of cool stuff like the Hope diamond, gem exhibits, dinosaurs, a giant squid, and race exhibits.
National Zoo – It’s been a long time since I’ve been to any other zoo, so I can’t compare the National Zoo to anything. It’s free to get in, and I think it’s pretty big. You can see lots of big cats, a giant panda, elephants, and zebras, to name a few animals. Also, it’s near plenty of great places to dine.
Smithsonian Castle – The Smithsonian Institution building, with displays of a little taste of each Smithsonian Museum.
Pay-to-get-in Museums*
Crime and Punishment Museum – Tickets are $20. Learn about the history of crime and punishment.
George Washington’s Mount Vernon** – Tickets are $15. Allegedly the most popular historic estate in the United States.
The International Spy Museum – Tickets are $20. I’ve been to this museum twice, and would certainly go back. The museum is devoted to spies throughout the world and throughout history.
National Geographic Museum – This museum doesn’t need an explanation – great rotating exhibits.
Newseum – Tickets are $22. I’ve been to this museum once and it was great. Exhibits include information about 9/11 and the Berlin Wall as well as fun exhibits devoted to First Dogs (Presidents’ dogs) or G-men.
President Lincoln’s Cottage – Tickets are $12. Located on the same grounds as the Soldiers’ Home, President Lincoln’s Cottage was the Lincoln Family’s residence for one-quarter of Lincoln’s presidency.
Monuments
Franklin Delano Roosevelt Memorial – Located at the Tidal Basin.
George Mason Memorial – Located at the Tidal Basin, near the Jefferson Memorial.
Martin Luther King, Jr. Memorial – Opened August 2011, located at the Tidal Basin.
National Mall – Spans the area from the Lincoln Memorial to the Capitol. Many Smithsonian museums are located along the mall, as well.
Tidal Basin – Partially man-made reservoir, home of the annual Cherry Blossom Festival, and location of many monuments.
Thomas Jefferson Memorial – Located at the Tidal Basin.
Washington Monument – Located at the end of the National Mall, viewable from the Tidal Basin. Currently closed due to damage sustained during the August 2011 earthquake.
Tours
Bike and Roll Segway Tour – We bought a Groupon for this segway tour and it was a lot of fun. The tour guide was really knowledgeable, and I learned a lot about DC. I would recommend doing a tour like this toward the beginning of a visit so that you can get a lay of the land.
*I have gotten into each of these museums for half-price after snagging a Groupon or LivingSocial deal.
**I have not yet visited this museum
My Life of Learning, Eating, and Living 
Hi, Lori. Thanks for this round-up of DC’s museums. When I first went to DC, we kept going round in circles not really knowing where to go first. 🙂 I’m bookmarking this as it’ll come in handy next time. Thanks again.