Is there a way to listen to the ending song again after I have beat the game? Other than the obvious way of beating it again.
PC ONLY :(
If you want to see the whole ending sequence and song, in-game, open the console ~ and run the command
You can extract the music as well using this method. Or you could probably just download it, the music's plastered all over the internet anyways.
Valve is making the soundtrack from Portal 2, entitled "Songs To Test By", available to download free.
You may need to wait for the correct volume to be released, but it will (should?) be there eventually.
Update: Soundtrack Volume 3 was recently released and includes "Want you gone". Plus there is a link to it as a ringtone.