Apropos of this weekend, there's "It's The End Of The World As We Know It"...
or if you want to be a little more depressing, there's "Childhood's End" by either Iron Maiden, Pink Floyd or, if you want to go a little more obscure, Marillion. Maybe a medley!
But seriously, there's "Forever Young"... oh, heavens... this is another one where any of the three would work... Rod Stewart, Bob Dylan or Alphaville.
Ok.. I officially suck at picking graduation songs... maybe because I never graduated. That might be it! *grin*