Pick one movie from each decade.

20's - Man With a Movie Camera
30's - M
40's - Double Indemnity
50's - Vertigo
60's - The Good, The Bad, The Ugly
70's - The Godfather
80's - Raging Bull
90's - Pulp Fiction
00's - Cidade de Deus

30's - Gone With the Wind
40's - The Third Man
50's - Seven Samurai
60's - Lawrence of Arabia
70's - Jaws
80's - The Abyss
90's - The Shawshank Redemption
00's - Wonder Boys

I limited myself to one from each decade but I could have gone with 5 or 6 from each decade as my favorite. This'll give you some of my favorites.

30s- The Wizard of Oz
40s- Citizen Kane
50s- Vertigo
60s- 2001: A Space Odyssey
70s- The Godfather
80s- Raiders of the Lost Ark
90s- Glengarry Glen Ross
00s- Batman Begins

god i hate all these cliched list where pulp fiction and godfather are always in the list.

30s- Mr. Smith Goes To Washington
40s- It's A Wonderful Life
50s- The Searchers
60s- To Kill A Mockingbird
70s- M*A*S*H
80s- The Right Stuff
90s- Schindler's List
00s- The Lord of the Rings trilogy

thats only on one list, mine. Also why don't you just post your own instead of threadcrapping?

20s - Pandora's Box
30s - The Wizard of Oz
40s - Casablanca
50s - Sunset Boulevard
60s - Psycho
70s - Taxi Driver
80s - Raiders of the Lost Ark
90s - Leon The Professional
00s - City of God

I have not seen enough movies from the 60's and before so I'm starting with the 70's.

70's - The Exorcist
80's - E.T. The Extraterrestrial
90's - Forrest Gump
00's - The Departed

50's - Rear Window
60's - The Graduate
70's - One Flew Over The Cuckoo's Nest
80's - This Is Spinal Tap
90's - Shawshank Redemption
00's - The Royal Tenenbaums

70's: Jaws
80's: Fast Times at Ridgemont High
90's: Tombstone

My favorites:

60s - Cool Hand Luke
70s - McCabe & Mrs. Miller
80s - Hannah and Her Sisters
90s - Sling Blade
00s - Lost in Translation

00s - A Trip to the Moon (Runner up - The Great Train Robbery)
10s - The Cabinet of Dr. Caligari (Runner up - Birth of a Nation)
20s - Nosferatu (Runner up - Metropolis)
30s - M (Runner up - The Public Enemy)
40s - Bicycle Thieves (Runner up - Double Indemnity)
50s - Seven Samurai (Runner up - Rififi)
60s - 2001: A Space Odyssey (Runner up - Psycho
70s - Taxi Driver (Runner up - Deliverance)
80s - The Thing (Runner up - Back to the Future)
90s - Fight Club (Runner up - Fargo)
00s - Memento (Runner up - Children of Men)

Not very unique, I know. It's hard reduce an entire decade to a single movie (which is why I added the runner ups).

20's - Metropolis
30's - M
40's - The Third Man
50's - Touch Of Evil
60's - Fail-Safe
70's - Monty Python and the Holy Grail
80's - A Christmas Story
90's - Before Sunrise
00's - My Sassy Girl (so far...)

It's silly that it bothers you. Those are two very good movies and it is only natural they would be someone's favorite. Both would make my top five for each decade.
These are what I consider "some" of my FAVORITES by decade (not necessarily the best movies) each is followed by an honorable mention:

40's: Casblanca/Citizen Kane
50's: Cane Mutiny/ Mr. Roberts
60's: Midnight Cowboy/ Night of the Living Dead
70's: The Man Who Would Be King/ Texas Chainsaw Masacre
80's: Amadeus/ The Thing
90's: Leon/ Glen Gary Glen Ross
00's: LOTR Trilogy

tough one.

70's - Jaws
80's - Empire Strikes Back
90's - Braveheart
00's - Almost Famous

*edit - had to change my '00 to Almost Famous (from Memento) when I realized it came out in '00.

1970's - The Godfather
Honourable Mention - Taxi Driver

1980's - Raging Bull

1990's - Pulp Fiction

2000's - Brokeback Mountain
Honourable Mentions - Almost Famous, The Departed

Pretty typical list:

20s - Metropolis
30s - Bride of Frankenstein
40s - Notorious
50s - Rear Window
60s - Dr. Strangelove
70s - Taxi Driver
80s - Raiders of the Lost Ark
90s - Pulp Fiction
00s - Lord of the Rings Trilogy

20s - The Cabinet of Dr. Caligari
30s - The Bride of Frankenstein
40s - Citizen Kane
50s - Paths of Glory
60s - Once Upon a Time in the West
70s - Dawn of the Dead
80s - Blade Runner
90s - Léon
00s - Before Sunset

1950s -> The Seven Samurai
1960s -> Easy Rider
1970s -> A Clockwork Orange
1980s -> Brazil
1990s -> Fight Club
2000s -> Children of Men

1930s - Mr.Smith Goes To Washington
1940s - Casablanca
1950s - Paths Of Glory
1960s - 2001
1970s - Barry Lyndon
1980s - Blade Runner
1990s - The Matrix / Dark City (Tie)
2000s - City Of God

Well, off the top of my head (runner ups are second)

20's - Metropolis / Nosferatu
30's - M / The Lady Vanishes
40's - Double Indemnity / Shadow of a Doubt
50's - North By Northwest / Ace In The Hole
60's - Night of the Living Dead / Dr. Strangelove
70's - Dawn of the Dead / Suspiria
80's - Evil Dead II / Blade Runner
90's - Glengarry Glen Ross / Ed Wood
00's - Shaun Of The Dead / City of God

So many things that were so hard to leave off...I think this is just about correct though.

60's - For A Few Dollars More
70's - Monty Python & The Holy Grail
80's - Aliens/The Thing (tie)
90's - The Silence Of The Lambs
00's - Kill Bill Vol. 2

I'll start from the 1950s, since I haven't seen enough earlier films to form an opinion:

1950s - Rear Window
1960s - The Graduate
1970s - Taxi Driver
1980s - Brazil
1990s - Fargo
2000s - Pan's Labyrinth (so far)

20's-Cabinet of Dr. Caligari
30's-The Mummy
40's-Sergeant York/Saboteur
50's -Rebel without a Cause
60's-Peeping Tom/Mask of Satan
70's-Halloween/Exorcist
80's-Re-Animator/Pee Wees BIg Adventure
90's-Fargo
00's-May

20s - The Passion of Joan of Arc
30s - City Lights
40s - Ivan The Terrible
50s - Pickpocket / Ivan The Terrible Part II
60s - L'Avventura / 8 1/2
70s - Mirror / Aguirre
80s - Dead Ringers
90s - Breaking the Waves
00s - Mulholland Drive