Actually, I could use this one to make sure I don't mess up my time zones when calling long distance, too--The World Clock Meeting Planner. From the Web site:
Need to make a call to someone far away? Need to arrange a videoconference, telephone- or net-based meeting with several people spread around the globe? This utility should help you find a convenient time, so that no one has to be up during the middle of the night.
There's also an the advanced meeting planner version, for coordinating with people in more than six cities.