Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
RSVPify - A powerful and awesomely customizable platform for selling tickets online for your event.
Facebook Local - Discover places to go and events happening near you
Online-RSVP.com - Beautiful online RSVP for wedding & other events. Create an online invitation, track your guests responses.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
TechEvents.co - Tech and startup events aggregator