Someone on Youtube describes Stellar by Incubus as the 'song of thier life', which I thought was pretty interesting -

It's not a concept I've ever thought about before, but I know exactly wht me meant.. the one song you feel an almost spritual bond with, that you love dearly, one that encapsulates and soundtracks your route through life to wherever you are now

for me, House Of Jealous by The Rapture holds so many memories it may as well be a family member, and Nothing Gets Crossed Out by Bright Eyes has massive emotional weight I feel like crying every time I hear it

you?