Gustav Holst, The Planets, Op. 32: VII. Neptune, the Mystic, performed by the Chicago Symphony Orchestra, conducted by James Levine.
Without a doubt one of my all-time favourite classical pieces. It transports me into an entirely other state of mind, quite away from anything of this world. Perhaps not the work of angels, as such, but the work of shadows and ethereal voices half-glimpsed and half-heard on the borders of dreaming sleep.