Arts & Industries Building
They're reclaiming the museum space at A&I, and showing some eclectic exhibits: two recent ones were Kente cloth and cultivated orchids.
Freer Gallery of Art and Arthur M. Sackler Gallery
One website does double duty for these two fantastic museums of Asian art, right next door to each other on the Mall.
Hirshhorn Museum and Sculpture Garden
The site is pretty cumbersome, but there's information about current exhibits and the permanent collection.
National Air & Space Museum
The capstone in the Smithsonian's collection, and the most-visited museum in the world. Great site with events, including IMAX movies.
National Museum of African Art
Built almost entirely underground, African Art is a hidden jewel on the Mall. They also do extensive educational programs.
National Museum of American Art
Closed until 2001 but making up for it with a fantastic website highlighting the collection. Don't overlook the smaller Renwick Gallery, where NMAA showcases American crafts and decorative arts.
National Museum of American History
Always a crowd-pleaser, the NMAH also has one of the best of the Smithsonian websites, with virtual exhibits and a "not just for kids" section.
National Museum of the American Indian
Although the actual building is still under construction, the site gives a good indication of amazing things to come.
National Museum of Natural History
The new Gem Hall and IMAX theatres are not to be missed, and the old standbys (like the big elephant) a should be part of every tourist's DC experience. Lots of hands-on events for kids.
National Portrait Gallery
Although it's closed for renovation until 2001, be sure to check out th resources on this lovely intimate museum's website. Marilyn Monroe and Andy Warhol were featured recently.
National Postal Museum
Although a short walk from the mall, it's a must-see! Exhibits of stamps, equipment and historic correspondence highlight our nation's postal history.