Kyrie by Mr. Mister is a killer tune if you are down with the 80s. Africa is pretty awesome, agree with the above poster. The Mexican by Babe Ruth is another classic, amazing track. It is so hard to pick just one.
I think if I could only listen to 1 song for the rest of my life it would be Walking on a Dream by Empire of the Sun. Not sure why other than it's fantastic.
That or Don't Stop Believin' by Journey.