Smart Rescheduler for Google Calendar
If you need to reschedule a meeting you've created in Google Calendar, you could look through participants' shared calendars to see when everyone is free—or you could enable Smart Rescheduler in Google Calendar Labs (which you access from the GCal settings menu), and let Google do the searching for you. Once enabled, Smart Rescheduler appears as a widget on the right side of the Calendar window; to use it, highlight the event you wish to reschedule, and click the Find a new time link. You'll get a list of alternative times, each with a Schedule This button to click for the time you choose.
