If your desk is tucked into a nook or corner and the cables are out of control, you can conceal the cords with a cheap beaded panel from a hardware store.
This Old House magazine offers this tip:
Run wiring behind a beadboard panel in the knee-hole at the back of your desk. Velcro the panel to blocking mounted on the rear legs or sides of your desk so that you can pop it off to access the outlet.
Since the panel is mounted with Velcro it is both easy to install and easy to remove when you need access.