Harry and Tonto
Nashville
One Flew Over The Cuckoo’s Nest
Network
A Woman Under The Influence
Harold and Maude
Fat City
McCabe and Mrs. Miller
A Clockwork Orange
Mikey and Nicky
The Godfather
The Godfather II
Next Stop, Greenwich Village
One Is A Lonely Number
An Enemy of the People
Sunflower
Five Easy Pieces
Chit-Chat On the Nile
Autumn Sonata
The Yellow Handkerchief
A Special Day
Taxi Driver
Annie Hall
Stroszek
A Brief Vacation
Dog Day Afternoon
Le Chat
Lulu the Tool
La Horse
Payday
The New Centurions
Blume In Love
Whity
Made For Each Other
Johnny Got His Gun
Serie Noire
The Conversation
Opening Night
The Fifth Seal
The Outlaw Josey Wales
The Last Detail
Mr. Klein
Nuts in May
Minnie and Moskowitz
Zandy’s Bride
Lies My Father Told Me
Wise Blood
Manhattan
Last Tango In Paris
Chinatown
Joe
Good list but missing quite a few that scream the 70’s.
Star Wars
Rocky
Poltergeist
Jaws
Patton
Animal House
Death Wish
Blazing Saddles
Monty Python and the Holy Grail
Close Encounters of the Third Kind
Deliverance
Apocalypse Now
The Deer Hunter
Other films that I think indisputably belong in a 1970s Top 50 missing from the OP
The Bitter Tears of Petra van Kant
The Black Stallion
Cabaret
Days and Nights in the Forest
God Told Me To
The Last Waltz
The Marquise of O
A New Leaf
The Spirit of the Beehive
Stalker
Straight Time
3 Women
The Traveling Players
Two English Girls
Walkabout
Btw, these are my favorites… Feel free to name as many as you can, or to criticize/praise some of my selections.
(I could see how this might be confusing for some)
you need to change the title to “my top 50 favorite movies of the 70s” so no one confuses it with something like "afi’s top 50 movies of the 70s "
The Taking of Pelham 1-2-3
Soylent Green
Twilight’s Last Gleaming
The Life and Times of Judge Roy Bean
Heaven Can Wait
Poltergeist is 1982 and verrrry much an 80’s film.
My own list would include the following films that haven’t been named yet:
The Conformist
The Discreet Charm of the Bourgeoisie
Cries and Whispers
The Exorcist
Barry Lyndon
Love and Death
Eraserhead
Nosferatu the Vampyre
Alien
Being There
Some others that I think are notable:
MAS*H
Klute
The French Connection
Fiddler on the Roof
Willy Wonka and the Chocolate Factory
Aguirre, Wrath of God
American Graffiti
The Sting
Alice Doesn’t Live Here Any More
Young Frankenstein
All the President’s Men
Halloween
Grease
Days of Heaven
Kramer vs. Kramer
Monty Python’s Life of Brian
What would you say characterizes a great 70s film? Cynical tone, dark cinematography, a rejection of 40s glamor, a lessening of the grip of Old Hollywood stars and directors, the total collapse of the studio system, the rise of the Spielberg/Coppola generation of directors? What am I missing?
I compared my personal Top 100 All-time List with films already mentioned and found one missing. It scores only 7.0 at IMDB but deserves better:
The Late Show
I needed a lot of Googling to get dates. Romeo and Juliet? No, before 1970. Officer and Gentleman? No, after 1979. Is there a good list of the 2000 most notable films with dates? 
I tried soon after posting it, but I am unable to edit.