I have visited HacDC a few times. Since I don't actually live in DC, I tend to just go when they have events. The people I've met there have always been friendly, and all of their events are open to the public.

They just started getting off the ground last summer, so it's not nearly as fancy as CCC or NYCResistor. Still, they put together some pretty cool stuff. Last time I went, I got to meet Mitch Altman.

Added a link to it,