Having a need to scan some documents while away from home I went looking for a solution that might make use of my iPhone's camera (and the lovely CamScanner+ app). I quickly came across a project to make one out of cardboard. You can now actually buy that stand but the person who created it won't ship to the UK. Boo hoo.
But they give away the plans for free. And so, after wandering around the streets of London looking for some home construction where I might find a very thick cardboard box being discarded by builders, I set to work printing, gluing and cutting.
I made two modifications: since my iPhone has a flash I made the hole at the top a lot bigger so the flash can illuminate the document; I also cut into the sides at the bottom so that A4 (rather than 8.5" by 11") could be accommodated.
Here's the final stand:
Here's a document scanned using ambient light (you'll see some shadows at the bottom and top as I made no effort to position this) with CamScanner+:
And here's another using the flash: