I just happened to answer that same question recently. I will post my answer again here:

I don’t know if there are are any designs meant specifically for a set using the 25GB discs. But I’ve had success playing around with the disc and cover designs already posted using other various artwork from this site, plus stuff you can find on fanart.tv. You can then use Gnu Image Manipulation Program (GIMP, which is free), to create your own homebrew covers and disc art if you don’t find any to your liking. Take a spin around the fan art section of this site and you’re sure to find lots of ideas.