Head on over to Portal 2‘s Official Website to download these outstanding pieces of music for free.
Valve has released the first volume of the soundtrack earlier today. The tracks that are included in volume 1 are:
1.) Turret Wife Serenade
2.) Science is Fun
3.) The Friendly Faith Plate
4.) The Courtesy Call
5.) I Saw a Deer Today
6.) Comedy Equals Tragedy Plus Time