Lauren sent in some great updates for our page about Washington DC (written by Staci in 2004):

Slow Travel USA - Travel Notes - What to See in Washington, D.C.

I will copy the additions here.

2006 Updates
Lauren Kahn (LSKahn), August 2006

For something unusual, try a Segway tour.
www.segsinthecity.net

DC's Cultural Tourism website will tell you everything going on during your stay.
www.culturaltourismdc.org

For an in depth tour, check the schedule at Washington Walks. They have some bus tours as well as walking tours, usually themed around subjects missed by the conventional bus tours. For example, they have tours focused on movies filmed in DC (you see "The Exorcist" steps) and Washington's Black community.
www.washingtonwalks.com

If you have kids, they will love a DC Ducks tour. Part of the tour is on land. Then the "duck", a World War II type land/sea vehicle, takes you for a dip in the Potomac River.
www.vacationsmadeeasy.com

Half price same day tickets to theatrical events can be found at Ticketplace, 407 7th St, NW (Archives Metro). Sometimes they sell tickets ahead of time as well. You can always check the night before to see what is available. Please note, tickets for the long running play "Shear Madness" (DC's answer to London's "The Mousetrap") are almost always available at Ticketplace.
www.cultural-alliance.org/tickets/