I have trouble getting the times right for meetings between myself and those on the west coast. This means that I'm a complete disaster when it comes to figuring out the best time to meet with those in farther off lands, like London.
That's where the World Clock Meeting Planner comes in. I put in all the cities that need to be involved in the meeting, and it gives me a nice and clean view of the best times to meet (with green hilighting, no less, to make the process idiot proof).
I'm fortunate that i2x has some over seas customers, and thanks to the meeting planner, I can even find times to meet at sane hours. As a bonus, the site also offers an international dialing helper, so that when it comes time to actually call my client for a meeting, I can figure out the right way to dial the phone (I know, trivial details).