Meetup.com

Meetup makes it easy for anyone to organize a local group or find one of the thousands already meeting up face-to-face. More than 2,000 groups get together in local communities each day, each one with the goal of improving themselves or their communities.
Meetup boasts over...
3600 active cities
5 million monthly website hits
4.7 million members
102,000 monthly meetups.