Well, lessee here, I haven’t seen . . .
The Shawshank Redemption
Life Is Beautiful
To Kill a Mockingbird
Paths of Glory (I was irked at missing this at my favorite local revival house)
Das Boot
Raging Bull
American History X
The Bicycle Thief
400 blows
The Graduate
Taxi Driver (though I think I’ve actually seen the whole thing, but only in little bits spread out over 10 years)
I’m sure there are more, but I thought I’d spare the rest of you from a list that is only taunting me.
Ive never seen any of the star wars movies. Just never managed to see them when I was younger now its more intentional.
the others are
Deliverance
Taxi driver
Ferris Buellers day off
The Hunt for Red October
I want to see Run Lola Run but I can only find it on rental dubbed which dubbing annoys me way too much. I also desparately want to see This is Spinal Tap but I cannot find it on video anywhere in town (I live in Nothingtown, USA)
The one time I tried to watch Citizen Kane I fell asleep about ten minutes in. I still have never got around to renting it again.
I’ve also wanted to see Chinatown, but never seem to remember to get it when I’m at the video store.
Easy Rider, Singing in the Rain
I was on a trip and it was playing yet where we went, but had finished at home before we came back.
Fortunately, it’s not like most series, where the plots are dependent on each other. I think I’ll rent it tonight, now that you reminded me. Thanks.
It would be quicker to list the movies I have seen. I like movies, but given the choice I’d rather read a book or just sit around and talk. Some of the movies people can’t belive I haven’t seen are:
Star Wars (I only saw the new one - it was okay)
Casablanca
The Godfather series
Top Gun (I don’t know if it is a good movie or not but I’m the only one I know who hasn’t seen it)
Most foreign films (Akira Kurosawa, Fellini, Bergman, ect.)
The Matrix
Most horror films (I did see The Blair Witch Project and it scared the bejesus out of me. Everything scares me.)
Most action films (Die Hard series, that series with Mel Gibson, ect.)
Ummm…I guess the only famous movie I have seen is Citizen Cane. It was pretty good, I thought. I keep meaning to get caught up, but it’s looking pretty hopeless what with all the new movies constantly coming out and all. 
[hijack]
silent_rob takes out a strange, rainbow-coloured, holographic card. It has a peculiar red pyramid with a large eye in the middle of it. He gives it to E d’Mann.
[/hijack]
I have never seen ‘Eraserhead’. Heard it was realy creepy, but none of my local video stores carry it.
Anything older than 1975, other than Sleuth and Wuthering Heights.
*Apocalypse Now
Grease, *uninterrupted
I have also been told I must see this movie but cannot find it at any video store.
Never heard of that one, heard of “Girl Interrupted” tho’… 
This is an excellent question, and a rather serious issue for me personally. Given my reputation as a film expert and my avocation as a movie reviewer, I’m very conscious of a few rather serious gaps in my filmgoing history.
To highlight a few already mentioned above…
Mentioned by Ukelele Ike: The Discreet Charm of the Bourgeousie and The Wages of Fear. (By the way, I agree that one can never see too much Bunuel. I’d also recommend you wait to see Bicycle Thief until you’re in a nice, neutral, open frame of mind; it’s quite a downer.)
By Hunsecker: Nashville. A major omission. Grrrrr. (And BTW, Miracle Mile is in fact a pretty good movie, although it hasn’t dated very well; the costuming is distracting, not to mention Anthony Edwards with hair, and the small cameo part played by Denise “Tasha Yar” Crosby" doesn’t work at all. Beyond that, it’s a killer movie.)
By sliv: The 400 Blows. Truffaut’s always been kind of an acquired taste; I’ve been working through his canon slowly. Day for Night and The Wild Child are both great, but I didn’t care for Fahrenheit 451 or Shoot the Piano Player.
By oldscratch: Kieslowski’s Dekalog. Good call. Meant to see it when a rep house in town programmed the whole thing, but… grrrr…
So those are the ones mentioned by others in the thread. Here are some additional titles I feel bad for never having seen:
Having mentioned Truffaut, I have to admit to never having seen what is generally regarded as his best film – Jules and Jim. Nothing against the movie, it’s just never been penciled on my calendar.
And speaking of French filmmakers, I’ve never seen Godard’s Breathless, the movie credited with launching the French New Wave into world consciousness. Another major gap.
And speaking of launches, I haven’t seen Scorsese’s Mean Streets. Can you believe it?
Another big one: Michael Antonioni’s Blowup. A quintessential film from a quintessential period of filmmaking. Haven’t seen it yet. Bad movie geek! Bad! No biscuit!
Another big one: Renoir’s The Grand Illusion. Regularly shows up on all-time top-ten lists. Doesn’t show up in my viewing catalog. Don’t make me turn in my film-buff membership card; I really will get to it eventually…
And although I wouldn’t call it a “good” movie, exactly, not like the above, Rollerball has such a cult following you’d think I would have caught it by now. Nope…
But this is probably the biggest omission on my list…
Billy Wilder’s Sunset Boulevard. I know, I know. I feel like I should be wearing a scarlet letter or something.
(Sigh…)
But I have seen the overwhelming majority of movies mentioned by other posters, and hey, I’ve also seen Shatner in Kingdom of the Spiders, so that’s gotta count for something, right?
Good luck finding Eraserhead. It was David Lynch’s student project when he was in film school, and is long out of print. I managed to see a third-generation copy it once, and count myself lucky.
Although many have seen it and hated every last minute of it, but I guess that kind of adds to the glamour of it for some of us.
I’m a hardcore movie buff as well. I once filled out a survey that included the question: “How many movies do you see a year? A. Fewer than five; B. Between five and ten; and C. More than ten.” I performed a quick calculation and wrote in 250.
I was without a TV or VCR for 17 years, during which time I got an awful lot of reading done. I also lived for a couple years around the corner from Chicago’s Music Box Theatre, when they had a different double feature every night. I went every single time there was a movie I hadn’t seen for over a year.
Then for four years I lived around the corner from a theater that showed a different double feature every week for $1.50–second run major release stuff. That way I managed eventually to see just about every movie released in those years. This is how I managed to discover hidden gems I might otherwise never have seen, like Groundhog Day and Miami Blues.
Now, for the past two years, I have a TV/VCR, and I continue to watch movies obsessively. I generally rent an average of, say, 5 movies a week.
Nonetheless, I’m constantly overwhelmed by the magnitude of the omissions in my life list. I recently saw Martin Scorsese’s “Journey Through American Film” (or some such title) and was amazed at how few I’d seen of the movies he referred to. On his “advice” I went out last week and finally saw Johnny Guitar, Leave Her to Heaven, Pursued, All That Heaven Allows, Gun Crazy, The Man with the Golden Arm, and Some Came Running.
And still, every time I visit the library or video store, I’m overwhelmed anew by how many movies I haven’t seen.
Major gaps: very spotty on Fellini, Bergman, and Truffaut. Still trying to wrap up Tarkovsky’s opus (he’s gotta be my favorite). Conspicuous missing checkmarks on my Peckinpah, Ford, Huston, and Fuller lists.
But for all this, my most compelling omission right now, this week, is–get this–Hollow Man. I’m a Verhoeven junkie.
(re: Eraserhead: try your library. If that fails, join Chicago’s Facets Film Center: they rent by mail.)
I’ve never seen Gone With The Wind. Not a minute of it. I’ll live.
Hey lissener, that’s a great list. I note you’re in Seattle as well; you and I should hoist a pair of brews and chat cinema. Maybe the next time someone more organized than I decides to put together a Puget Sound Doper get-together.
P.S. Re Verhoeven – What do you think is his best film? Spetters, Soldier of Orange, or…?
I knew it. I knew I shouldn’t have come back to this thread, or my movies I have to watch list would just keep growing longer.
I’ve searched in vain to find a copy of Ace In The Hole but no one seems to have it.
Haven’t seen Some Like It Hot, though I love Wilders other stuff.
I’d love to see Eraserhead, but barring that, I should see Wild At Heart.
Also:
Life is Beautiful
Guess Whos Coming to Dinner
A Streetcar Named Desire
Annie Hall
Dirty Harry
Body Heat
etc.
Cervaise: Thanks for the Miracle Mile rec. Go see Sunset Blvd. Go now! 
I have never seen E.T.
Now after so many years I refuse to see it just to be stubborn.
Zero Hour.
Zero Hour is the movie that provided the inspiration for Airplane!. Since Airplane! is my most favoritest movie of all time, I must must must see Zero Hour some time before I die.
But damn it, Zero Hour has never been released to video! What do I have to do, call up all the cheapo independent TV stations and see if any of them have it in their 3 A.M. inventory?! Sheesh!