Charlie Murder's soundtrack is one of the best parts of the game, which admittedly has a lot of good parts overall. The soundtrack is a punk rock homage performed by Ska Studios' James Silva and Michelle Juett Silva (and friends), and it's available to download for "anything you want," from $0 to whatever your wallet can handle.
There's also a classy, three-track vinyl edition available for $10 or more, featuring the songs "Mnemomic Atomic," "I Vote 4 Chaos" and a cover from Ska's previous game, I MAED A GAM3 W1TH Z0MB1ES 1NIT!!!1, "For Yr Pain." Purchasing the vinyl automatically nets you a download of the full Charlie Murder album, so you may want to consider the two-for-one.