PPTC is a good place to start. They usually have cue sheets for the rides. There is also an on-line cue library, but they just made that members only.
Also look at the Oxon Hill Club
http://ohbike.org/
http://bikewashington.org/ is another good resource
Waba is an advocacy group. They're not much into rides.
Lots of good riding in upper MoCo and lower Frederick Co, especially around Poolesville.
Howard County, Prince George, Annarundel.
Or you can cross the river at White's Ferry or one of the bridges and ride in Loudon Co. Good rural roads with lots of hills.
edit - opps, I was thinking that you were in upper MoCo
Close in to DC - Beach Drive. Hains Point. MacArthur Blvd to River Road
Some good hill riding in Arlington and Falls Church (Williamsburg, Military, Chesterbrook, Kirby, Idlywood, etc)
Good back roads in Alexandria, especially down by Mount Vernon. And thru Annandale and Barcroft.
Try Loudon County, starting at Leesburg. I like to follow the Reston Century (August) route. Several 1000's feet of climbing.
Or just start riding the DC streets. Explore.