This user at BitsOfMyMind.com shows us how they took an Ikea Antonius 6-hook hanger and turned it into an under-desk mounted cord-wrangling gutter (It's the next best thing to using a real rain gutter, you know!).
All you need to do is mount an Ikea Antonius hanger rack to the underside of the desk using long enough wood screws.
After that, all your cords and power strips can rest comfortably inside the cradle you've created. Use more than one of these 20 1/2-inch long racks if your desk space needs it!