I recently got a 3D printer and one of the first projects I undertook was to create an iPad holder prototype for the LinnStrument. After a few trials, I designed one that works great and that is printable in three parts. It works from the iPad 1 size all the way up to the iPad Air, including iPhones (the 6+ works quite nicely). Since the LinnStrument can be bus-powered from all iOS devices with a lightning connector, this is a really nice standalone expressive music-making combo imho.
Here are some pictures: