Hunter - Find all the email addresses related to a domain
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
AnyMailFinder.com - Find anyone's email address
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Norbert - Norbert is an online tool that helps you to find anyone’s corporate email address.
Bigtent - BigTent is a web-based organization and communication portal for groups.