Usually for me, it's songs with foreign Lyrics I can't understand. When a person's voice can convey the emotion without you even having to know the lyrics, that is the mark of a GREAT song.

Some of My Favorites are ;

Gotoz A Ran From the Blackhawk Down Soundtrack

Llorando by Rebekah Del Rio

And I've been jamming "Hemmorage" by Fuel a lot lately!