DC Area Resources
One of the most helpful and active communities for DC-area film and video is the Women in Film and Video (WIFV) listserv. It’s invaluable, and you don’t need to be female to use it! You do need to be a WIFV member, however. In addition to the listserv, WIFV holds a number of get-togethers and great educational events year round. It is a great first stop for learning more about the DC area production scene.
Other great DC-area resources:
Stage 32 is a social network and education hub for film, television and theater creatives. I've found a number of interesting articles and blog posts about subjects such as screenwriting and distribution on the site. The Stage 32 community is very active!
Staff Me Up is quickly becoming a valuable resource for people looking to hire crews or for crew people looking for jobs.