kennedy space center and when you're in DC, the NASA air and space museum....also in DC the lincoln and jefferson memorials, the vietnam memorial (although it probably won't speak to you the same way it does to me), the washington zoo...
i also love the library of congress, but mainly to use it.....i did all of my research there for my dissertation....great place...
i adore DC...my husband was born and raised there, and still thinks it's the center of the universe....
as for orlando, i can't imagine not wanting to spend all my time in WDW....
if you have kids, there's a fun place on I drive but i can't remember the name...it's an upside down building....maybe it's called wonderworks....my kids really enjoyed it....
and then there's skull kingdom, but we've never gotten up the nerve to go there...i seemed to have convinced them this past summer, but they still chickened out...