If it has to be Opeth then "Epilogue", "Creedence" or "To bid you farewell".
If it doesn't necessarily have to be Opeth then:
http://www.ultimatemetal.com/forum/showthread.php?s=&threadid=29505
I have a few additions to that thread though:
Oscar Peterson: Wheatland
Dusty Springfield: Summer is over (the title fits a little)
Stevie Wonder "Golden lady" & "They won't go when I go" (REEEEALLY sad)
Marvin Gaye: Life is for learning (the title fits a little too I guess)
Lee Hazlewood: Wait and see (the text fits I guess. At least the text I've noticed. I don't really pay attention to lyrics).
Sam Cooke: "A change is gonna come" (I guess the text fits a little too)
Procul Harum: In held twas in I: a) Glimpses of Nirvana (I guess the title fits a little too).
Lee Hazlewood: "My autumn's done come" (I guess the text + the title fits a little too)
Lee Hazlewood: "Bye Babe" (I guess the title fits a little too).
Love: "Everybody wants to live" (I guess the text fits a little too)
Crowded House: "Don't dream it's over" (I guess the title fits a little too).
Cris Williamson: "Last sweet hour" (I guess the title fits a little too).
Henry Mancini: "A day in the life of a fool"
Mozart: Requiem (The title says it all)
Cream: World of Pain (The title says it all as well)
Queen "The show must go on" (The title says it all as well)
Nancy Sinatra (John Barry): You only live twice (The title says it all as well)