As for other films, I'd say check out
IMDB's top 250 list.
I haven't seen em all....but I've seen a good two thirds at least. A lot of crap in there, but there is a lot of great films there too! The important thing is being able to tell the difference!
(LOTR...better than Kane!?
)
More specifically, absolutely anything by the Coen Brothers. Each film of theirs is a masterpiece! Fargo especially, one of my favourite films of all time.
Other unmissible Coen brothers treats include The Big Lebowski, O Brother Where Art Thou and The Man Who Wasn't There.
Also rent a few films by Lynch. Love him or hate him, his films are still worth watching to get an idea of what people are talking about...personally I love him! Get Blue Velvet, Lost Highway, Eraserhead and Mulholland Drive in particular. Stay away from Wild at Heart, that was pretty boring!
Rent everything by Hitchcock. There's no question about that!
Rent everything by Kubrick. Another director who released nothing but masterpieces. Especially:
2001, Strangelove, Clockwork Orange, The Shining, and Full Metal Jacket.
Eyes Wide Shut wasn't nearly as bad as many people make out, but it was certainly his weakest moment.
Rent anyhting by Fincher...except maybe Alien 3...that film was butchered by the ignorant "suits". It's suckiness cannot be fairly attributed to Him. Get Seven and Fight Club in particular. See Panic room for an example of a wasted opportunity.
Kevin Smith has already been mentioned. My advice: Watch his films in order.
Clerks - Mallrats - Chasing Amy - Dogma - Jay And Silent Bob.
P.T. Anderson makes damn fine movies! Get Boogie Nights, Maqnolia and Punch Drunk Love.
Get Being John Malkovitch and Adaptation, by Spike Jonze and Charlie Kaufman. Don't ask questions...just do it damnnit!
Tarrantino...yeah you've already seen all his films....worth a mention though just in case....
Requiem For A Dream and Pi, by Darren Arronofsky. Great films.
Find out what John Woo was like before he moved to Hollywood. Watch Hard Boiled and The Killer, and see how they measure up to the likes of Broken Arrow. No contest. Face/Off was pretty damn cool however.
And then just for a laugh, rent some Troma movies. Get Terror Firmer...their absolute finest moment!
and just some random movies that come into my head:
Spinal Tap
Donnie Darko
Memento
Twelve Monkeys
Dog Day Afternoon
Gattaca
Amelie
Royal Tannembaums
Ghost World
Very Bad Things
Lock Stock and Two smoking Barrels
L.A. Confidential
Crouching Tiger Hidden Dragon
The Usual Suspects