In case someone didn't already say it in this thread, there are three codes.

1. Early Access Code (Only works for the Early Access time period)
2. Serial Code (Register on Square Enix MEMBERS site)
3. Registration Code (Product Code) *PS3 people need to enter this code on the PSN Store under "Redeem Codes" - PC people can use the Mog Station site

Also, if you came to this post and skipped ahead without reading, you may want to go back and read what others have said. There is some helpful info listed.

Good luck!