I was informed by Shellshock929, that Pepsi is running a promotion with Rock Band. On specially marked pepsi bottles, the inside cap, reveals a code that can be redeemed online for Rock Band prizes. One of the prizes is A free download, I don't know if entering this "drawing" is a guarenteed free song, but i just got "Don't Stop Believeing." (You choose the song from their list)
And hey, $1.69 for a 1 Liter and download is cheaper than a $2 Download.