The ones that deal with abandonment or otherwise leaving someone behind always kill me.
Like in "When She Loved Me," I always start to break down when the scene fades to Jessie and Emily in the car, just like old times, and Jessie is in heaven. Then you can see the confusion on her face as they get out, and then the devastation dawns on her as Emily drives off after leaving her by the side of the road.
And her line "You never forget kids like Andy or Emily...but they forget you" is like the final punch to the gut.
http://community.livejournal.com/ltd_brands_suck/