The Time Machine
Professional looking clocks, skinable calendar, atomic synchronizer and organizer. The Time Machine is a massive set of components and functions, completely covering all the tasks of managing your computer clocks. That includes managing appearance of clocks, display of various time zones,... - Highly customizable digital and analog clocks with a powerful skin engine; - Integration of the clocks in a Windows environment.
http://www.atlantsoft.com/utils/store/ttmsetup.zip - 4Mb - Download - Screenshot

Ace Clock XP
AceClock is a skinable transparent desktop clock with organizer and stickers, skins support, atomic internet time synchronization, fully customizable see through display with tooltip and convenient interface, it is designed to suit any and all your needs. ... You will get voice time spelling in multiple languages, powerful alarms with templates, upcoming alarms, quick reminders, countdown and stopwatch timers, universal calendar with date calculator, different time zones support with reliable atomic clock synchronization and much, much more.
http://www.aceclock.com/files/aceclockxp.zip - 2Mb - Download - Screenshot

Elprime Clock Pro
Elprime Clock Pro is a compact program to synchronze your computer with any computer on your Local Area Network or one of the hundreds Atomic Time Servers. It is skinnable analog clock transparent both in Windows 2000/XP and Windows 95/98/Me!. It also comprises an advanced alarm scheduler and a... The clock is fully skinable and comes with a lot of nice-looking skins already. ... It also supports other useful features such as sounding chimes and starting with the system. ... At the same time, the tool doesn't come heavy on your system, using just a fraction of system resources.
http://www.elprime.com/ElprimeClockPro.exe - 2Mb - Download - Screenshot