Every known Pokedex 3D AR code, compiled by GBATemp. If you point your 3DS camera at this image, the app will a) freak the hell out, b) find three new Pokemon for your Pokedex, and c) fill your sticker book with unknown Pokemon (the result of already having found three in a day). Fun!
You can also explore this code generator by Ravenworks, which seems to come across some “unknown” Pokemon as well, like this one. These, I think, are actually “unknown,” as in, currently unimplemented… or something.
[Via Pokedex 3DS]