Though I know it's a trendy song right now, I think 21 Guns by Greenday suits CoE very well. The defeat in it, especially couched in somewhat soldierly symbology works for me in a representation of Jack's defeat and desolation. It's about giving up and ... well, I sort of have to give up on canon in Torchwood to preserve my fannish like of it and since I'm not willing to give up Torchwood yet as a fandom ... canon's got to go.

As my partner said after listening to me go on about CoE; got a toothache? Blame RTD!