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