Bicycle Thieves - One of the most important films ever made, which means there's about a 1 in 10 chance I've seen it. I should get right on that!
The Graduate - People apparently got so caught up in the youth culture hype and the subject matter in 1967 that they didn't realize that this movie is clearly about a doofus who doesn't know what he's doing, both at the start of the movie and at the end of it. Go read the two Ebert reviews (from 1967 and 1997) if you don't believe me. I for one thought it was obvious enough. The movie is fine as it is, but the old AFI list having it as the seventh best movie ever made was probably a bit ludicrous.
Carrie - The De Palma one? It's been one of my 10-15 favorite movies since I was 14. The book remains an all time favorite as well. Remember that it's both horror and slightly kitschy comedy at the same time. You can probably skip both remakes. I don't think De Palma has any better movies, either.
Stand By Me - Loved this when I was younger but I'm not particularly convinced it's held up. Mainly because it seems really obvious that the kids are reading movie dialogue. It doesn't bother me that it's schmaltzy really (The Princess Bride, far more beloved, is actually a lot worse with that sort of thing IMO.)
Inception - Decent as a thriller and a concept, but the emotional resonance in the movie is like dead zero. Not even really one of Nolan's better films and that weird period where everyone was debating about how the rules worked and such when it came out now looks really dumb.
The French Connection - I like this quite a bit now but it is, as Joe said, because of the interestingly bleak and ugly depiction of NYC circa 1970, which seemed like it would have been a pretty new thing in movies. And because of Popeye Doyle, simultaneously a hero cop and total douche. And yes the chase scene, though the creepy ambiguous ending is perhaps the best part IMO. Be advised that the first time you see it, it's going to seem really disjointed and incoherent, so put the f***ing subtitles on.
Duck Soup - I don't know a freaking thing about the Marx brothers!!
Shane - Urgh, I really should've seen this one by now.
The Usual Suspects - I like the twist if only because the Spacey character is essentially amusing himself. And the "GIMME THE KEYS @#W($*@U$" lineup scene is funny. Otherwise, the popularity of this movie is pretty mystifying--it has so few entertaining scenes and digging through the movie to see how Spacey's story checks out is about as much fun as digging through a haystack, not finding the needle, and then stepping on the needle somewhere in the barn on your way out and contracting Hepatitis F. God, I'm hilarious.