one thing I always wanted to build but probably never will (other things being more important) was to have a company that used 3d printing to make stylish frames for glasses. Why you ask, because it's a pain to find good styles when you have either a big or small head, it's not that good styles don't exist, just that since your not a significant enough market for them to mass produce it your mostly ignored having to settle on ones that just happen to be in your size. Plus you could totally have retro and strange styles and since you don't have inventory stocked the sky's the limit on how many styles you could keep in your inventory.
I just can't focus on this idea since I have other ones to pursue (the ones more akin to my lifes work sort of thing) so feel free to rip me off, maybe if you do you could toss me a pair of frames for free ;)