There are plenty of Web services out there designed to ease the pain of group scheduling, but most have their own annoyances, such as requiring you to create a user account -- or worse, forcing everyone else to log in, as well. I've found an alternative that's painlessly simple.
When is Good shows you all the times that work for all your invitees, so you can pick the best option. I really like the fact that there's no need to log in or create an account (though an account does give you additional conveniences). Just visit the site and, one click later, you can paint the calendar with potential meeting times.
You'll get a link you can send to your invitees. Again, no need to log in -- they just mark the available hours with times that work for them, enter their name, and send the response.
In the end, you can see which times are most convenient and pick the winner, which you can even import into your iCal-compatible calendar.
When is Good has lots of little goodies, like the ability to select time periods in increments as short as the quarter hour. It's time zone-aware, and you can even customize the URL that gets sent to invitees. The service is similar to MeetingMade, which we discussed a few months ago. MeetingMade has a more polished interface, but both get the same job done - and MeetingMade shows every sign of not being free after beta, so I suggest you give When is Good a try.