Been geeking out about this leaked trailer all morning.
It was supposed to show on the next episode of Marvel's Agents of S.H.I.E.L.D. but it got leaked so they just released it.
You can find it here: http://www.comicvine.com/articles/avengers-age-of-ultron-trailer-update/1100-150169/#ftag=YHF6f45a36