We visited DC in May of 2011 and wanted to see the Washington Monument, but had no intentions of going inside and riding the elevator to the top! I am somewhat terrified of heights, but once we approached the monument, there was a woman handing out free tickets and we said, "Alright, let's do it!" We stood in line for about 15-20 minutes (DC is always crowded in MAY) but I didn't mind at all. Apparently the tickets are free regardless (nearly every attraction in DC is) and you just have to get there early in the morning to nab you one or two.
The ride to the top was the most interesting part of the monument! The elevator has panels of glass on either side and the tour guide stops every few seconds to point out all the historic inscriptions in the stones that built the monument. VERY cool. Once you're at the top there is very limited space so if you are claustrophobic at all you may want to think twice about this! However, I am scared of heights and did just fine. The few windows at the top are so small that you really don't realize how far up you actually are. The view couldn't be better, however, for you can literally see all of DC in every window you peer through!