There's a whole album of them here
http://imgur.com/a/EFOqsScanning a Pokemon's QR code does not make it spawn or, as far as we know, have any affect on its spawn rate. All it does is add the pokemon to your pokedex as "seen" so you can check its habitat.
Each QR code you scan gives you 10 points towards an island scan. When you do an island scan, it causes a rare pokemon that doesn't normally spawn in-game to become available somewhere on your current island. There seems to be some limitations as to what pokemon can spawn this way, and each island has a different set of pokemon that can spawn from an island scan, but more testing is needed to get something like a comprehensive list.
When you do an island scan, it tells you what route the rare pokemon is on and then you have 60 minutes to find it before it stops spawning. It seems to become a pretty common spawn in whatever route it's assigned to. You only have one chance with the rare pokemon, if it faints, then tough luck, so try to capture it. Also, if you haven't progressed through the story yet, it's possible for the pokemon to spawn in a route you can't reach yet, so don't do an island scan until you've cleared a whole island.
The number of QR scans you can do is limited. You can bank up to 10 QR scans available and you get new ones at a rate of about one every two hours, so you can do roughly 1 island scan per day.
