I dug out my original Xbox, and realized that many of my games lacked cases. While I didn't have any spare full-size Xbox-style cases handy, and my local game store doesn't yet have a shipment of Xbox-like cases in, I do have a lot of cheap jewel cases. A ton with front artwork spots, so that was the main focus, but also some with a spot for rear artwork.
So I created a Photoshop template to help make it all consistent. The end result...
The templates include all of the ESRB ratings already in the correct spot, so you can just show/hide the layer for the rating you want.
The fit of the back template is very snug, some trimming may be required. It ends up looking a little something like this:
Both can be printed on 5x7 photo paper, and fits a standard (whatever that means) jewel case. To keep the front slip in place, I recommend putting a tiny bit of tape on the inside, over the bits that it slides under.