Yeah I'm not too familiar with Chantilly.

Have you thought about contacting Evolution Cycling to find some routes (not for commuting--just general rides)? I think they tend to go out of Reston.

Then there's the Haymarket team, which is supposedly a pretty good group.

There's also a club that rides in Warrenton (Warrenton cycling..? but they may be part of Haymarket now..) if you want to trek out to some more rural areas.