Clock Tray Skins is a good pack of themes for the Windows Clock which will allow you to give it a new look and change its boring aspect.
It includes more than 120 different ready-to-use skins which we'll be able to use o decorate our desktop. Each skin can be configured individually and show different features.
One of them even allows you to set it as a counter clock, so you'll be able to know how long the computer has been on.
Clock Tray Skins also includes an attractive calendar, some shorcuts, allows you to set transparency levels,...