In case you missed it (we certainly did), Valve have released a physical version of the Portal 2: Songs To Test By soundtrack collection.
The release, available from Amazon for £13.72 (it's still listed with a November 26th release date by other online retailers) includes a fourth CD alongside the three volumes already freely available in digital form on the game's official site. The fourth disc contains thirteen tracks from the first Portal - including the original Still Alive track, along with an alternate take of the piece by Jonathan Coulton.
Contained within the package as well is the "Turret Lullaby" mini-comic (also previously available digitally.), and key codes for Team Fortress 2 and DOTA 2.