Doodle is an online scheduling tool that can be used quickly and easily to find a date and time to meet with multiple people.  First you suggest dates and times for your event participants to choose from, then Doodle creates a polling calendar that can be sent to participants for feedback.  As each participant selects the dates and times from the polling calendar that he or she is free, Doodle aggregates the responses and tells you which option works best for everyone.