For events with a year or more lead time, choosing a date isn't too difficult; attendees will find a way to work around it. But when planning just a few weeks out, it can be impossible to find a day when a large portion of attendees won't already be doing something else. For those gatherings, try WhichDateWorks.com. All the attendees get the chance to fill in dates that are good, bad and so-so, and the winner is picked democratically. It's a free service, and registration isn't required.