FadingTaskbar gives you the ability to manage your taskbar's transparency level.

You can control the transparency of your Windows taskbar having it show only when you hover over that area with your mouse cursor. FadingTaskbar supports individual transparency settings for when the mouse is inside and outside the taskbar. It can be set to fade in and out but can make the taskbar solid when maximized windows exist.

FadingTaskbar will remembers the original transparency and provides quick access to your system's taskbar and start menu properties. It is straightforward to deploy and use effectively cleaning up your desktop. The fact that it is portable is just another useful bonus.