Quite surprised to not see the two that came immediately to my mind on here yet, though there's plenty of others that have challenged my tear ducts as I read through - some without even having to hear the song.
Anyway, my two are:
Boys of Summer by Don Henley
and one that I only know from a band formed of my old teachers (Wilbury Jam), but appears to be originally by Jaki Whitren called Give Her The Day
I can't sing either of these songs, as my voice just cracks.