Bring Your Daughter to Work Day - Aperture Science Psychoacoustics Laboratory [Songs to Test By - Volume 2]
Volume 2 is out, and you can get it for free here! Along with Volume 1.
Valve is a great game developer and you should support them by buying any of their stuff. The complete pack there includes Portal 2 and is only $50! You get all their games. All of them. For the price of just Portal 2.