There is another ASPCA commercial with "Answer" playing over it — "Cast me gently into morning, for the night has been unkind" — combined with a montage of abused animals.
"I Will Remember You" is probably one of the saddest "goodbye" songs one could ever listen to, and has been used for two different series finales: Melrose Place and Felicity. It can be a very powerful tearjerker for people who have lost someone.
And for Buffy the Vampire Slayer fans everywhere, "Full of Grace". Although, even without that association, this song is sad enough. Add in that ending, and it only gets worse.
Then there is "Fallen".
And "Hold On", which came about when she was hearing about a HIV-negative woman who was watching her lover's slow death from AIDS.