It could be anything from Frozen to the musical episode of Buffy the Vampire Slayer. I'm a huge Les Mis fan, and this one gets me every time:

Not really knowing anything about Les Mis, I was dragged kicking and screaming by my mum to watch it for the first time, and I left a blubbering mess. I'm pretty sure I cried through half of the film, and to this day that song gives me goosebumps every time. ABC Café does the same thing to me. As does I Dreamed a Dream. Valjean's Soliloquy too. And On My Own... I'll stop now.