Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Eventjoy - The Easiest Way To Organize An Event
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Flyer by Paperless Post - Fun to create. Easy to share. Totally free online invites.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Event Hunt - Startups and Tech Events Curated By Locals