I don't know about you, but I find myself constantly switching between time zones throughout my working day as a translator. I've found a really useful tool to help with this. Here it is:
Google time operator
In Google, simply type 'time' and the name of a city and you'll get the current time in that city. You can do this for any city around the world.
Of course other options include having a collection of clocks on your wall for quick reference (or, if you have a Mac like me, on your Dashboard). You could also make use of this website for a comparative view of time zones in major cities around the world (I have this bookmarked). But for speed and ease of use, the Google time operator is a very handy tool I think you'll agree!