DS Phat using only ribbons and a placemat. The inside flap even holds three game carts, though we can't vouch for the sturdiness of its grip.
We see these table pads at Bed Bath & Beyond all the time, as well as a lot of other potential materials, so head over there if you're looking for some DIY case ideas. Or, you know, if you need new window treatments. Check past the post break for another photo of the placemat pouch.