Like many device, Nintendo DS also needs to be protected by something. Not your pocket, the elegant Professor Layton Nintendo DS Case should be a good choice.
The DS case has a brown shell with black interior coming with several little pockets, and the drawing of Professor Layton is printed on the surface of case.
The case is available in two colors, brown and red, and each costs $20.9 USD. You can get it at NCSX.