I've found that the best way to keep time zones straight is to use Google Calendar for scheduling in my home time zone (Japan) and TripIt for scheduling whenever I am out of the country -- more on that here.

The built-in world clock on the iPhone is really handy. I also use the FoxClocks extension for Firefox to keep London, New York and Tokyo time in the status bar of my web browser. London generally goes on daylight savings at the same time as the rest of Europe, and New York generally goes on daylight savings at the same time as most of the US (Indiana and Arizona excluded), so it's pretty easy to add or subtract hours from those two bases.

Usually I see people say something like "8 am New York, 1 pm London, 8 pm Hong Kong, 9 pm Tokyo" when scheduling a conference call, which is pretty clear for everyone.