This was a triumph...
If the first volume of the Portal 2 soundtrack wasn't enough for you, Valve has now released the second volume to tide you over until the third one is released.
Here's the typically tongue-in-cheek invitation-slash-announcement from Valve: "Give your ears the gift of sound and let them relive the glory days of testing in full fidelity, without the distracting hisses and pops that accompany being submerged in acid. Songs to Test By: Volume 2 (of 3) is now available for download. Plus: Free!"
As with the first volume, the Portal 2 soundtrack "Songs to Test By: Volume 2 (of 3)" is totally free to download through here. It contains 18 tracks all bundled up in a single zip. You can also get ringtone versions if you want to customize your iPhone or Android mobile device. In case you missed the announcement the first time, the first volume of Songs to Test By is also still available for download there.