I like the montages where they make weapons out of junk, or are training.
Some of the ones I remember was the weapon-making in Phantasm II where Reggie makes a 4-barrel shotgun.
In Commando with Arnold and Rae-Dawn, where they break into the gun store and gather an arsenal.
And in Army of Darkness where Ash creates his metal hand and boosts the castle's defenses.
A good training montage is the Rocky IV one where it contrasts Rocky's basic down-home training to Drago's more modern and chemically enhanced training.
Also, I liked the montage in Revenge of the Nerds where the nerds find and fix up their frat house.
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Here's a link to a montage of a bunch of different movies. Not just one.
The Ultimate Movie Montage | I Am Bored