Here, you'll find two scripts: Carve-It and Chrome-It, which can render some truly nice artistic effects on grayscale images.

Drop Shadow will cast a shadow behind your selected object. It has three important parameters. X and Y offset determine where the shadow will be placed in relation to the selected object. Offset is measured in pixels. High values make the shadow look like it's far away, and low values will make it look closer to the object. The blur value is also important, because a shadow that is cast far from the object has a higher blur level.

Perspective Shadow has a very important parameter: the perspective angle. If this angle is set to 0 or 180, there will be no shadow, because the script assumes that the object has no thickness. This also means that this script looks fine in certain angles, but unnatural in others. The other parameters are quite self-explanatory. You'll get more blur if the horizon is far away, and the shadow length is the length in relation to the selected object.