Weekend getaway in the DC area?

There's also Harper's Ferry which is just over the border into West Virginia.  Not sure what it's like at Christmas time but in nice weather it's great for hiking about and such.  I imagine the Poconos are probably too far to go?
I've been to Cape May but in the month of May.  The victorian houses can be outrageous, the most colorful town I've ever been to.  It's on the beach and I've heard at Christmas everything is lit up with Christmas lights.  They have some very good restaurants in town.
I used to go to Bethany Beach when I was a kid so have been up to Rehoboth and it is nice.  You also have Ocean City 20-30 minutes south if you want a bigger city atmosphere although a lot of places might close down in the off season.
Not sure what else?  Get some crabs while you're over there!  Btw, my all time record of eating crabs in 1 sitting was in Delaware - 23.  So close to the 2 dozen mark.

Thanks for your suggestions! I kicked around Williamsburg and you're right, it would be beautiful, but it's a bit far from my parent's, about 5 hours. I'm definitely into the beach idea, so I think we're going to Cape May. They have some Christmas things going on, it's about 3.5 hours from my parent's, and it's the beach!

We live in Jamestown, about 2 miles from Historic Jamestown and the Jamestown Settlement.  They will just be concluding the celebration of our 400th anniversary around Christmas time.  Both Jamestown and Colonial Williamsburg are particularly entertaining, and for some reason, very attractive to Brits.  I know because my wife is one.  Also my next door neighbor has a son in Cape May.  Winter can definitely be iffy there in December. 

Williamsburg and Jamestown are only about 2 and 1/2 hours from D.C., straight down I-95 to I-295 to I-64.  Weather is rarely a problem here.

Thanks for the tips! We're actually going to be at my parent's in PA, so Williamsburg is a bit further than I wanted to go, but it would have been perfect. Maybe next time! 

And as for picking crabs....I lived in Baltimore for 8 years and I never acquired a taste for it.    I love crab everything except one I've just picked myself! I think it's too much work for so little reward. I know...blasphemy! 

Oh, the reward is euphoria!  The fresh crab meat picked right from it after it has been freshly steamed is delicious!  Good luck in your holiday hunting, sounds like Cape May is a winner.