Because the availability of codes can change, I won't list hundreds here. However, here is a method to get you started immediately.
Now that you have keys, you might be tempted to rush to Fyrestone at Level 5 and start popping them open. borderlands goty golden keys
"Ah, Vault Hunter," Dr. Zed said with a sly grin. "I see you've made it. I have a special reward for you and your fellow adventurers. You see, I've been tinkering with some... shall we say, 'extras' that Gearbox Software has been kind enough to provide. Behold, the Golden Keys!" Because the availability of codes can change, I