For the global visualization of time zones and clocks on your desktop (freeware):

Desktop Sun Tracker 

http://www.herethere.net/dt/

This software displays two versions of the world map, a day, and a night version, and fades between them to show which portions of the world are in daylight, and which aren't. In other words, this is a dynamic wallpaper that updates based on where the sun is relative to the surface of the earth.

Breitling World Time

http://www.breitling.com/en/misc/bwt/

A time panel featuring 6 settable clocks, UTC (GMT), miniature global sun tracker, currency convertor, time arithmetic calculator, and units convertor (skip the flash intro and then click on Breitling World Time at the bottom line).

Personal World Clock - Java Applet - up to 25 Locations

http://www.timeanddate.com/worldclock/personalapplet.html