I hate scheduling, especially with people not in my company. The back-and-forth e-mails and phone calls are maddening. I have eagerly tried many solutions to this hassle, none of which did what I needed, and I've been awaiting what I thought was the holy grail of time finders, TimeBridge, since I wrote it up last year.
TimeBridge is still in deep, dark, private beta, but there's another schedule helper that just popped up, iPolipo.
iPolipo integrates with Outlook. It knows what times you are available by synchronizing with your calendar, and then it lets you block open times as reserved for meetings yet to be set up. (Thankfully, it does not just assume that any open slots are available for meeting requests.) When you want to meet with a person, you send him or her an invite via the iPolipo plug-in, and they then get a link to a page that shows the times that you've marked as available to new meetings, and that haven't already been nabbed by other people.
You can set up different groups and block different times for them. The blocks can overlap. For example, say you're a professor. You can set 1:00 to 2:00 p.m. each Wednesday as available for meetings with other faculty, but 1:00 to 4:00 p.m. for students. When you send out a request for a meeting, you select which group the recipient is in. Or you can invite a person to have ongoing access to your calendar, and they can then request a meeting with you. They will only see the times available to the group that you've placed them in. Once someone requests a spot, and you confirm it, no one else can grab it.
I have not tried the service for setting up a meeting with more than two people.
I really like what iPolipo does, although I would not recommend the version I'm trying now. In order to invite someone, you have to type in their entire e-mail address, which is an annoying step in an e-mail plug-in. There are other minor usability snags as well. But a new version should be out Monday, which CEO Hari Shetty demoed to me today. It lets you easily attach an iPolipo meeting invitation to an ordinary e-mail that you compose in Outlook, and it has other welcome UI improvements and new features. It is definitely worth waiting for.
Be prepared to pay for this service, though. iPolipo starts at $99 a year after a 30-day free trial.