In order to accommodate the various cords and cables, and allow for ventilation, an entertainment center I built has a number of cutouts for clearance. Although the size of these cutouts varies, I used the same general procedure to make all of them. Using the back panel as an example, start by drilling a 2"-dia. hole at each corner of the cutout.
Next, using a jig saw, I cut away the interior waste of the cutout. The key here is to cut close to the layout line, but remain on the waste side.
Finally, to smooth out the rough-cut edge, I used a router and a straightedge guide. I simply clamped a straight piece of hardboard along the layout line. Then using a pattern bit, I trimmed the waste flush. The result is a cutout with straight, smooth edges and nicely radiused corners.