Any film involving animals really that doesn't end too well. So naturally Disney animated films set me off.
The film that gets me most emotional is Homeward Bound though. And I can't link again atm so here is the link to copy and paste is anyone wants to.
I just get so emotional at the end when the animals return but Shadow even there and his owner boy Peter starts to believe that he didn't make it, and then.. oh god its so beautiful and tears tears tears.
Another happy animal ending with Two Brothers. The story of two tigers seperated as cubs and both raised in different ways. One by a family until he got to be too big and the other in a cage trained to fight. They do end up meeting in a ring and the timid family tiger doesn't want to fight and the other one is ready to pounce then after a few swipes they remember each other and they end up playing and biting playfully and its lovely. The crowd goes mad and a riot ensures (I think, not watched it in years), then the brother tigers escape, find their old home and they find their mother who was believed to have died when they got captured as cubs. And oh happy tears again.
Yeah I can't watch films about animals, happy or sad without just bawling my eyes out.