Since 3DS games come with that little notch that makes it impossible to use any of your old DS cases to store them, I've been looking for a good case solution. It looks like Tiny Cartridge helped me find one.
AmiAmi is selling the case you see below, which stores 5 3DS (or regular DS) games for 800 yen (about $10). I don't think it would be all that comfortable to keep in my pocket, though.
Source: Daily News from GamePro.com