Eventjoy - The Easiest Way To Organize An Event
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Conferize - Conferize is a web platform for finding and following conferences.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
B12 Bookings - Bookings scheduling software that integrates with your site
Meetabit - All the local tech and startup meetups in one place - easy to organize & attend