1. Right-click on your taskbar and click on Properties
2. Click on the customize… button as seen below:
3. This will open the Notification Are Icons. At the bottom there are two links, click on Turn system icons on or off:
4. Now from the dropdown select Off for the Clock (1st item)
5. This works the same in Windows 8, simply follow step 1-4 and the clock will be gone from the Windows 8 taskbar
Now you can add more icons to the Windows 8 taskbar. The clock can be restored the same way.