Good website for finding a common time to have a meeting?

I find that there’s frequently too much back-and-forth e-mailing with clients and other parties when I’m trying to find a good time to meet. I’m looking for a web service that will gather available times amongst multiple people and find a commonly available meeting time.
I’d like something that’s easy to use. No registration required, and a clean page design is preferred.

I’ve tried:
ScheduleOnce, TimeBridge, and TimetoMeet but the process is just too complex and seems to take longer than sending the typical e-mail exchange…