A recent thread compiled the perfect list of songs that say, in one way or another, that everything will be OK. This playlist will make you smile and remind you that whatever is going on, it too shall pass.
update: I tried with all my songs and yes I know it doesn't work with every song. I just think it works if you play the song on time or it works with some sort of upbeat song. But yea, it doesn't work perfectly like you would expect.