Harmonix is giving away "a free song" for the first 2500 players who Join and complete the "Free DLC Code Challenge".
Simply join the challenge, get 30 stars playing Rockband Blitz songs, and then check your completed challenges summary in RockBand World (Facebook) for your code.
I did this for the XBox 360 and got 160msp (which is actually good enough for 2 songs right now). I'm not sure how this will redeem for other platforms, but post if you find out.
Update: The 2,500 codes are split as 2,000 for Xbox 360 and 500 for Playstation 3. USA Only.
Simply join the challenge, get 30 stars playing Rockband Blitz songs, and then check your completed challenges summary in RockBand World (Facebook) for your code.
I did this for the XBox 360 and got 160msp (which is actually good enough for 2 songs right now). I'm not sure how this will redeem for other platforms, but post if you find out.
Update: The 2,500 codes are split as 2,000 for Xbox 360 and 500 for Playstation 3. USA Only.