This was a gift for his tenth birthday - he was also receiving a DS, so I knew it would immediately be put to good use!
I used a light courdoroy as the outer fabric and a pumpkin-coloured fleece for the guts. I sewed in two deep (by DS game standards) pockets in after the fact, and made a wrist strap for it as well. I was especially proud of the strap, as it showed more foresight and planning that I usually exhibit in my sewing. I may actually be getting good at this thing!
I made up the pattern, using my own DS as a template. I didn't want to use too much velcro, as the stuff that I bought out of a bargain bin has incredibly hold-power, and I have to wrestle with my wallet that I made a little too often. I did do a test run with my own DS though, inserting it into the cosy then flailing it about wildly by the wrist strap. I can safely say that this baby is solid.