When Aron successfully breaks his arm, and he spends several seconds yelling in both triumph and pain.
Aron walking free of the canyon, getting help from a hiking family, and watching the rescue helicopter arrive, with Sigur Ros's "Festival" belting out over it all.
Also a somewhat grotesque Crowning Moment of Funny: The climax of the film, when Aron succeeds in cutting his own arm off in order to escape from under the boulder that's trapped him for five days. He staggers a few steps away...and then he stops, turns around, pulls out his camera, and snaps a picture of it before leaving for good. Exhausted from fighting to stay alive for five days, starving and dangerously dehydrated, just finished wrapping up his new bloody stump so he'll have a shot at surviving the trek back out, and he still stops for a souvenir picture of the rock that almost killed him. The feeling of triumph in that moment is almost indescribable.
Made even more awesome by the fact, that this actually happened. This photo exists.
Not quite as spectacular, but his method of getting his knife back after dropping it out of reach is a great early sign of his ingenuity.
The climax of the film itself: probably the first time in cinema history where self-mutilation is equal parts horrifying AND inspirational!
Wow... so it is possible for that sentence to exist.