Online Booking Systems

Try 
Booking
Easy ticketing for any event. Sell tickets within minutes. You can have your tickets on sale today! (Australian based)
Booking Bug   "Don't change your business, change your booking system." This does a lot more than just booking events.
EventBrite   Make your event a success

Eventbrite empowers you with simple but powerful tools to manage, promote, and sell out your event. It's free to sign up and get started.