There are two moments of TV that I have watched that always make me cry.  Always.

1: The transition between season 3 and season 4 of Lost when Charlie dies in the 3 finale, and then in the 4 premier when Hurley and Claire start crying.  That ALWAYS gets me.  And believe me, it's not just tearing up, it's crying like a baby.

2: The season finale of Grey's Anatomy season 2 when Denny dies.  I haven't seen it in a while, but when I did, I didn't cry as much as with Lost, but I cried a hella lot.