If you own the Wii U and 3DS versions of Super Smash Bros. you can get a free soundtrack CDs, but you need to act fast.
Right now, you can get a two SSM soundtrack CDs at Club Nintendo by registering both versions of the game on the site. There are two CDs featuring dozens of tracks from the game. The offer is valid through January 13th (this coming Tuesday). This will also register you to receive the previously announced Mewtwo character DLC (that offer is open through March 31).
For more details on how to register, go to Nintendo's official site.
The soundtrack CDs are a nice offer, but I do think it's odd how many hoops Nintendo is making people jump through just to get one free DLC characters – especially considering that you have to spend $ 100 on both versions of the game just to receive it.