Eventbrite.com is the best event registration service I have found. Features include... 

• FREE EVENTS - It's free to you when you are not charging for your event. 
• PAID EVENTS - Easily except payments. The per-ticket charge is minimal. You can also pass the fee along to your attendees.
• EXPOSURE - Your event is included in their directories, categories, locations, and rss feeds. sample 
• SOCIAL - Easily promote your events on your social networks. more 
• INTEGRATE - Easily add your event registration to your website. more 
• Mange attendees, create coupon codes, track stats, print badges and more. See all the video tutorials and FAQs.