Because this thread is being pointed to in a reply to another thread today, allow me to add:

1) Buy a MetroRail day pass for $6.50 -- allows you to hop on and off anywhere on the DC subway system (Metro) anytime after the morning rush hour during weekdays and all day weekends and holidays -- details at http://wmata.com/riding/passes.cfm#Metrorail

2) At the same site, scroll up and notice the $3.00 one-day bus pass -- hop on, hop off the DC bus system all day!

3) Across the street to the south of the Lincoln Memorial is the FDR memorial. All of my tours for out-of-town guests include it and they love it. It is an outdoor memorial, always accessable. Great view of the tidal basin, cherry trees and the Jefferson memorial as well. The FDR memorial is here (you can zoom in and out).

4) In the spring, look for the Annual Garden on the patch of ground shown here (you can zoom in and out) -- fabulous display of many varieties and colors of tulips that bloom somewhat before the cherry blossom peak.

5) If you want to get out of the city, see George Washington's home at Mt. Vernon. Thankfully, Maryland has not yet allowed any development of the land on the other side of the Potomac River across from Mt. Vernon so that the view is much like what our first President experienced. Their website is here.