Kind of Free: Sign up at Club Nintendo & Register Products/Do Surveys for Rewards
This isn't quite a full blown freebie, but it's a very cool nevertheless. If you head over to Club Nintendo, which has recently opened to North America, you can sign up and earn coins. You earn coins by registering products you own and completing surveys. Coins can then be converted into rewards.
If you have an existing "My Nintendo" account, you can login and follow the instructions to covert. The site is experiencing a lot of traffic right now, but we were able to sign up and login successfully after a few attempts.
Registering a Wii game is good for 50 Coins, a Nintendo DS game for 30 coins, and a Wii Shop Channel game/Wii Channel for 10 Coins. Currently, potential rewards include items like the Game & Watch Collection for Nintendo DS for 800 coins, a Nintendo DS Lite Case (Silver) for 400 coins, Mario Party Playing cards for 500 coins among others.
*borrowed*
https://club.nintendo.com/
If you have an old account just do the surveys and you will get the points for the already registered games as it lets you link. Easier than looking up old codes : ) Just sign in rather than register to start