I'm not a movie fan at all, but there is some that I absolutely loved. I'm not gonna include comedies because everyones humour is different (Freddy Got Fingered is the funniest piece of television I have ever witnessed). If you haven't seen them, I'd recommend:

The Shawshank Redemption (obviously, but I think you have seen this already and you had better shown him by now )
12 Angry Men
The Apartment
The Matrix (the original was a complete film, the sequels I didn't get)
District 9
Big Fish
Dead Man's Shoes (you can watch this on YouTube)
The Blair Witch Project (I'm not into horrors and this wasn't like a Scream movie where a guy jumps out of a closet and frightens the trout out of you, it was just spooky)
Avatar (which everyone has seen)

I could go on but those are what I'd recommend. I know for a fact that anyone within reason would have a an amazing time looking at them.