Beach Drive takes one north through Kensington, Maryland, beyond the beltway and into the suburbs. The easy and normal approach is to ride it to the end and head home, a nice 25-miler from NW DC.
On a longer day one might cut west across Bethesda, connecting with River Road en route to Poolesville. It's a good ride. Not, though, on a weekday morning, when traffic is not pleasant and cars are not respectful. (As well trained as DC drivers are on weekends, they are surly on weekdays. I guess some people are just pissed to be heading to work while I'm out for a ride.)
So for the first time I continued straight from the end of Beach, picking up Dewey to Viers Mill, then Turkey Branch Parkway, connecting to Independence and Parkland in Wheaton Maryland. This is a collection of residential through-streets and school zones that made for empty roads and quiet pedaling. Zooming in on the map shows lots of possibilities for extensions from here. 36 miles or so includes an extra loop around the lollipop head at the far end.
[In truth, I've been on these roads before. There was a gosh-awful 200K permanent from Bethesda that Sam and I did in 2006 on a super hot day. Sam may recall - he was on a cheap Bikes Direct fixie with spokes that kept working loose. Pretty sure that route had us on these same roads, for a while at least.]