From Hunt Taylor:
A small windoid shows the current screen coordinates of your mouse, current coordinates within the top window, optional changes in screen coordinates, and the RGB and Hex color values of the screen directly underneath the current mouse point.
Completely rewritten. Genuinely floats above all windows, without interfering with your work. Optionally floats only above a specific application, hiding when it is not in front. Vertical or horizontal window. Nicer interface.