Evite
www.evite.com
Create an event, send professionally designed invitations to your community and track RSVPs all for free.

Meeting Wizard
www.meetingwizard.com
Send one email to find the best date & time that works for the most number of people for a meeting or conference call easily and quickly with this tool.  Meeting Wizard will also allow participants to propose alternate times, update you with each response, send out confirmations and automated meeting reminders.

Doodle
www.doodle.com
Similar to Meeting Wizard, with better time-zone support.  Doodle also allows you to create an open link to the survey, allowing anyone to respond as opposed to only invited guests, and you do not need to sign up for an account.

Timebridge
www.timebridge.com
Lots more functionality than Meeting Wizard or Doodle.  Timebridge can sync with participant's Outlook, Google or iCal calendars, send automatic email or text reminders, and even help you stay on track with your agenda.