Dan,
Looks like the weather is going to be pretty nice -- I would have been happy to host you at my club, but am not going to be able to get out this weekend.
If access isn't an issue, my personal favorites in the greater DC area are RTJ, Columbia, and Burning Tree (primarily for the experience). Congressional is IMHO a very very solid course, but it doesn't have anything that makes it really special, which is probably a reason why it's not favored on GCA. Note that I haven't played some of the newish courses like Lake Presidential or laurel Hill.
If you're going to be in Alexandria, Belle Haven was recently redone, and you might be able to get on -- it's not great, but it's very convenient. Army Navy isn't too far and has some cool holes, and Mt Vernon is also convenient.
Finally, there have been threads in the past about the lack of really top-tier courses here, which is unfortunate but true.
Carl