Download Portal 2: Songs to Test By (volume 1) for free
Move over Lady Gaga, here comes LaDY GLaDOS. While the latest Jonathan Coulton single will still cost you, Valve has posted 22 tracks - totaling more than an hour - of Portal 2's electro-trippy ambient soundtrack for free download, complete with album art and Android/iOS-formatted ringtones. Even if you're not a Portal fan, this is worth grabbing for tracks like Science is Fun and the hauntingly catchy Turret Wife Serenade.
Bonus: the fact that this is labeled "Volume 1" implies more free tunes will be coming sooner or later!