Using Inkscape I imported a vector drawing of the 360 gamepad by grumbel on the Open Clip Art Library as the basis for the outline of the controller, resized it to the dimensions on the Wikipedia page, and made 12 copies of it (since that's how many controllers the club owns).
The slots for the games were just rectangles using the dimensions from another Wikipedia article. I discovered that I had to convert these objects to paths (under the Path menu in Inkscape) before I saved the file as a DXF file (or PDF file, depending on which CAM program you're using).
I converted the drawing to G-code for a 1/2 inch end mill as a roughing pass, thinking that I'd then do a finishing pass with a smaller bit, but decided that it was good enough after the first pass. I milled it from two inch thick extruded polystyrene foam (Styrofoam), then cut it down to size on a radial arm saw (which explains the mistake you see on the side in this last photo).
Not bad for my first successful CNC project, if I do say so myself.
Edit: I also published this an an Instructable.