TheAeroClock is a nice Desktop Clock

The Aero Clock is a simple and beautiful desktop clock that displays the current system time. Although, you can view the time on Windows Start Menu, this beautiful clock with alpha transparency can add a bit aesthetic appeal to your desktop.

The program is also portable so no installation is needed. Just run the program and the clock will appear. It will display the time as an analog clock display along with an optional seconds hand. The size and transparency of the clock can be customized. It also comes with a lot of textures using which its appearance can be modified. It can stay on top of other windows or you can lock it into a single place.

The program is a freeware and runs on all the version of Windows. It is also portable.