If you've been looking around the internet for Destiny-related material at all, you might have already come across these. If you haven't, they're totally worth looking at, especially those ones for the emblems and the armor-color altering shaders.
You can just go over to the Destiny website, set up your account, and then start putting them in. They're totally open and don't get used up from someone entering them, so feel free to take them all and pass them around. Be sure to keep an eye out for any more codes that are coming out, or let others (especially me!) know if you find any more.