If we're going all patriotic epic songs, then it is obviously this:

Swansea City fans sing Hymns & Arias at Wembley 2011 - YouTube
http://youtu.be/BaAmz7Dx2ic (I was about 50 yards to the left)

Nothing better than being at the Liberty and hearing Hymns and Arias being belted out. Sends chills down my spine just remembering it at Wembley.