Meetup.com helps you make new friends by connecting you with people in your community who share your interests or hobbies. It is not a dating site, but a way to meet people to enjoy your passions with. More than 400 Meetups are active in the Washington, DC metropolitan area. Check out Washington Meetups
Meetup organizes groups with interests ranging from knitting to politics to sporting activities to music to scrapbooking. Members receive e-mail notifications of upcoming events for their selected groups. The site is free for members but if you organize a new group there is a $19 charge.