No more than 3 days or so, hopefully in the spring of 07...

My priorities in going to DC with my wife are to see both "campuses" of the Smithsonian Air & Space Museum.

Neither of us has been to DC before, we'd like to see other touristy stuff, but really, the Smithsonian is the real reason we're going, ie: if we see nothing else, we'll be somewhat satisfied.

Are there any other "must-sees" that we should work into our trip, given that we'll likely be spending a full day or two half-days at the above museums?

Thanks in advance for your help and suggestions!

Incidentally, we'll be flying in from YXU to YYZ to IAD, return.