Party with a Local - Party with a Local is a free app that connects travelers with locals that want to party.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Project Fixup - Meet people, not profiles
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Palaround - Meet people you should be friends with.
Bigtent - BigTent is a web-based organization and communication portal for groups.