I've got two of my favorites.
First, The Main Title Theme from Mass Effect:
It just makes you feel small, and like your problems are just one of many that everyone goes through. Like your problems have been dealt with before by others and that you aren't alone. It always gives me the feeling that other people are experiencing what I'm feeling. Good or Bad, I'm never alone.
Now this is the only song in a game that has actually made me want to rush to the boss and smack him in the face.
First time I heard it, I nearly did before realizing my party had ZERO as far as supplies.