The Mass Effect 3 soundtrack has been available for almost as long as the game itself, but it was only available on Amazon and other retailers. It's out now for iTunes for $6.99.
If you've yet to listen to the soundtrack, you can grab it here. Buying the songs individually would cost you around 22 dollars, so it's not a bad deal.
Cris Velasco, Sascha Dikiciyan, Sam Hulick and Clint Mansell contributed to the soundtrack. "Das Malefitz", the credits track by Canadian band Faunts rounds up the album.
Amazon also has the soundtrack for $5.99, if you'd like to pay a dollar less and don't feel like worrying about getting it in your iTunes database.
It's unknown whether the upcoming Reckoning DLC for Mass Effect 3 will come with additional music for the game. You can read about that here.