After reading Wildfire’s thread, I had to do a take-off of my own, since I’m all about the 70s anyway. 
So, instead of trying to make a huge long list of what all I’ve already seen, I’ll just let you guys make suggestions and then come back and clarify what I’ll need to catch up on. And you don’t have to worry about them being seminal or anything, just as long as you like 'em and can tell me why.
Now, I’m off to get my hair cut. I’ll check back in tonight. Thanks everyone!
Some of my favorites:
Annie Hall: “Oh yeah? Well, I just happen to have Marshall MacLuhan right here!”
Nashville: I wasn’t very familiar with Altman when I first saw it, and was blown away, especially by the perfect ending.
Badlands: Because no one films grass quite like Terrence Malick. And I have an embarrassing crush on the young Sissy Spacek.
Airplane!: “I can make a hat, or a brooch, or a pterodactyl!”
For my money if you feel like getting a little groovy your best bet is going to be
Mother, Jugs & Speed or
The Pom Pom Girls - There’s one line that my family still quotes 25 years after a chance TV viewing.
and if TV movies count:
Murder on Flight 502 - Farrah Fawcett, Sonny Bono, Robert Stack, and Danny Bonaduce (and many other folks you’ll recognize). Polyester and Aquanet abound!
The Seven-Ups- far superior to the similar French Connection.
As a kid on vacation with my family, this film was the the holy grail of in room movies. I never actually saw it and had always assumed that it was a porn.
So far out of the ones mentioned, I haven’t seen The Pom Pom Girls (intriguing – can you give me a brief run-down?), The Seven-Ups or, I think, Murder on Flight 502. I’ll have to see if I can find them. As to the others, Badlands is a particular favorite and I rather enjoyed Mother, Jugs & Speed when I watched it earlier this year. Who knew The Cos had once been actually hip!?
Probably nobody remembers it nowadays, but back in the 70’s there was a little movie called Star Wars that lots of us kids went to see…
The quintessential '70s New York City film: The Taking of Pelham One Two Three. Brilliant lines like: “Screw the goddamn passengers! What the hell did they expect for their lousy 35 cents - to live forever?”
And:
Mayor’s wife: I know a million dollars sounds like a lot of money. But just think what you’ll get in return.
Mayor: What?
Mayor’s wife: Eighteen sure votes.
Mayor: All right, all right. Warren, Warren, arrange for the payoff!
Oh, and Dog Day Afternoon for a double feature.
Stranger
The Godfather 1 and 2
Taxi Driver (the other quintessential New York City movie of the '70s)
American Graffiti
Aguirre, the Wrath of God (1972)
Ali: Fear Eats the Soul (1974)
Alien (1979)
All That Jazz (1979)
Amarcord (1973)
American Graffiti (1973)
The American Soldier (1970)
Annie Hall (1977)
Antonia: A Portrait of the Woman (1974) (documentary)
Apocalpyse Now (1979)
Badlands (1973)
Barry Lyndon (1975)
The Black Stallion (1979)
Blazing Saddles (1974)
The Buffalo Creek Flood: An Act of Man (1975) (documentary)
Cabaret (1972)
Chinatown (1974)
Chulas Fronteras (1976) (documentary)
Close Encounters of the Third Kind (1977)
Coffy (1973)
The Conformist (1970)
The Conversation (1974)
Day for Night (1973)
Days of Heaven (1978)
Death in Venice (1971)
The Deer Hunter (1978)
Deliverance (1972)
The Discreet Charm of the Bourgeoisie (1972)
Don’t Look Now (1973)
Enter the Dragon (1973)
Eraserhead (1978)
Fellini’s Roma (1972)
Film Portrait (1970) (documentary)
Five Easy Pieces (1970)
Frank Film (1973) (short)
The French Connection (1971)
Fuji (1974) (short)
The Godfather (1972)
The Godfather, Part II (1974)
Halloween (1978)
Harlan County U.S.A. (1976) (documentary)
Harold and Maude (1971)
Hitler: A Film From Germany (1978)
Hospital (1970) (documentary)
The Hospital (1971)
Jaws (1975)
Killer of Sheep (1977)
King: A Filmed Record (1970) (documentary)
Lacombe Lucien (1974)
The Last Picture Show (1971)
MASH (1970)
Manhattan (1979)
McCabe & Mrs. Miller (1971)
Mean Streets (1973)
Multiple Sidosis (1970) (short)
Nashville (1975)
National Lampoon’s Animal House (1978)
Network (1976)
Hapax Legomena I: Nostalgia (1971) (short)
O Lucky Man! (1973)
One Flew Over the Cuckoo’s Nest (1975)
The Outlaw Josey Wales (1976)
Patton (1970)
The Phantom of Liberty (1974)
Powers of Ten (1978) (short)
Reminisces of a Journey Through Lithuania (1972) (documentary)
Rocky (1976)
The Rocky Horror Picture Show (1975)
Scenes From a Marriage (1973)
Serene Velocity (1970) (short)
Shaft (1971)
Solaris (1972)
The Spirit of the Beehive (1973)
Star Wars (1977)
The Sting (1973)
Straw Dogs (1971)
Taxi Driver (1976)
That Obscure Object of Desire (1977)
Thieves Like Us (1974)
The Tin Drum (1979)
To Fly (1976) (short)
The Tree of Wooden Clogs (1978)
A Woman Under the Influence (1974)
Woodstock (1970) (documentary)
Young Frankenstein (1974)
A Clockwork Orange
Rollerball
(Plenty of good ol’ ultra violence.)
Good grief, that is so high on my list of best movie moments ever.
Five Easy Pieces; One Flew Over the Cuckoo’s Nest; The Last Detail.
For Nicholson fans in particular.
Are you (the OP) looking for any movies made in the 1970s that people like? If so, that could end up being quite a list.
I’ll second a vote for Network, a personal favorite. Not only was it made in the 70s, it perfectly captures the malaise of the period.
Also, a vote for Breaking Away, if you want some optimism with your pessimism.
From 1970 a little film called
MASH
From 1971
Dirty Harry
Billy Jack
Plus a bunch other I am too tired to search for.
Lessee, done did its have strike throughs…
Thanks for all your suggestions. Needless to say, I’m heading to the IMDb right this minute to see which ones I’ll be adding, especially the foreign.
The word in Cabaret was actually “screw”.
For those who have answered during my epic post…
*Got both of those Rysdad. Alex is an all-time favorite character and who could possibly resist James Caan??
*Peak Banana: I liked the bit about how they have too much sex yet he never gets any. Heh.
*vivalostwages: The only one I haven’t seen out of those is The Last Detail. Is that a must for someone who usually can’t stomach Jack?
*And Bytegeist, I fell in deep like with Fade to Black just because of Dennis Christopher. What happened to him anyway?
*To Thudlow: 'course I’ve seen SW silly rabbit.
*To Rick: All them too.
*Stranger: I haven’t seen Pelham, but DDA is pure genius! “Attica!” “Attica!” Ah, Pacino pre-scenery chomping days. I miss him like that. 
*BBVL: As a member in good standing of the I Love the 70s club, I can assure that none of those have escaped my attention.
So it’s all good folks. Keep 'em coming. I’m making a list, but not checking it twice because I trust you guys.
[ETA to Walloon: All our memories can’t be that good. Just only focusing on the most important part (sex!) my brain recognized. Damn getting older. :o ]
Wow, that’s a lot of good movies. All I can think to add is a little Ralph Bakshi - Wizards - 1977.
And for some campy, badly dubbed spaghetti-western fun, there’s the Trinity movies - They Call Me Trinity- 1971, and Trinity is Still My Name - 1972.
Alien (1979, U.S., dir. Ridley Scott)
American Graffiti (1973, U.S., dir. George Lucas)
Amarcord (1974, Italy, Federico Fellini)
Annie Hall (1977, U.S., dir. Woody Allen)
Apocalypse Now (1979, U.S., dir. Frances Ford Coppola)
Barry Lyndon (1975, U.K., dir. Stanley Kubrick)
Cabaret (1972, U.S., dir. Bob Fosse)
Carrie (1976, U.S., dir. Brian De Palma)
Chinatown (1974, U.S., dir. Roman Polanski)
A Clockwork Orange (1971, U.S., dir. Stanley Kubrick)
The Fantastic Planet (1973, France, dir. Rene Laloux)
Five Easy Pieces (1970, U.S., dir. Bob Rafelson)
The Godfather (1972, U.S., dir. Francis Ford Coppola)
The Godfather Part II (1974, U.S., dir. Francis Ford Coppola)
Jaws (1975, U.S., dir. Steven Spielberg)
The Last Picture Show (1971, U.S., dir. Peter Bogdanovich)
Macbeth (1971, U.K./U.S., dir. Roman Polanski)
McCabe & Mrs. Miller (1971, U.S., dir. Robert Altman)
Monty Python and the Holy Grail (1975, U.K., dir. Terry Gilliam, Terry Jones)
Monty Python’s Life of Brian (1979, U.K., dir. Terry Jones)
My Brilliant Career (1979, Australia, dir. Gillian Armstrong)
Nashville (1975, U.S., dir. Robert Altman)
One Flew over the Cuckoo’s Nest (1975, U.S., dir. Milos Forman)
Play it Again, Sam (1972, U.S., dir. Herbert Ross)
Play Misty for Me (1971, U.S., dir. Clint Eastwood)
Rocky (1976, U.S., dir. John G. Avildsen)
Saturday Night Fever (1977, U.S., dir. John Badham)
Seven Beauties (1976, Italy, dir. Lina Wertmuller)
The Seven Samurai (1954, Japan, dir. Akira Kurosawa)
Star Wars (1977, U.S., dir. George Lucas)
Taxi Driver (1976, U.S., dir. Martin Scorsese)
The Tree of Wooden Clogs (1978, Italy, dir. Ermanno Olmi)