Use Twtvite to organize Tweetups, manage a Tweetup group for recurring events, and sell tickets online.

Let users RSVP in different categories, for example: attendees, sponsors, etc.
Invite friends via email or Twitter or send updates / changes about an event.
Sell tickets directly from your event page. No per-ticket fees!
Let people find your Tweetup Group and keep in contact with your attendees.
Twtvite is FREE to use.
The plans below are only if you want to : sell tickets, send invitations / announcements, collect email addresses.
The founder answers all support questions and emails personally. Here are some ways to get in touch with us: