Transformers was a fun movie with awesome effects, but I was too old when the toys and cartoon came out, so I missed the whole nostalgia thing.
American Beauty annoys the crap out of me.
Never saw Dark Crystal. I can't get a grasp on whether or not this is a cult classic. I think I remember it not doing well, even among fans, when it came out. I think I have seen zero pop culture references to it, unlike all the other movies on this list. (then again, i never saw it)
I love Psycho very much. I had the rare treat of seeing a screening in a real theater with my wife who knew absolutely nothing about it. Didn't even know The Twist. (She's Japanese, not hopelessly ignorant).
But I had to admit that if I had one DVD in each hand, I would go for Aliens. Even the alienless first half is great. Even the spunky, precocious kid is great.