Vanilla sky
The Ninth Configuration
Good Will Hunting
High Fidelity
Wild at Heart

1. Chasing Amy
2. Jackie Brown
3. Leon The Professional
4. Infernal Affairs
5. Irreversible

Ghostbusters
Back to the Future
Terminator 2
Batman Begins
Harold & Kumar Go to White Castle

1. The Godfather
2. There Will Be Blood
3. Brokeback Mountain
4. Pulp Fiction
5. The Departed
6. United 93
7. Almost Famous
8. The Godfather: Part II
9. The Insider
10. The Incredibles

1. Fast Times at Ridgemont High

In no particular order:
Jaws
Star Wars
Raiders of the Lost Ark
The Empire Strikes Back

This is one of those topics where I can't give a definitive answer. I love so many films that it's hard to narrow my favorites down to just five.

Having said that, I'll give it a shot...

1. Seven Samurai
2. The Big Sleep (1946)
3. The Petrified Forest
4. Goodfellas
5. Dr. No

Those are pretty representative of my favorite movies. There are probably another 20-30 movies that I'd like to list, but it is a TOP 5 list per the topic, so....there you go.

Leon The Professional
Taxi Driver
The Big Lebowski
Back to the Future
Casablanca

Honourable Mentions: A Bout de Souffle, There Will Be Blood, Boogie Nights, Out of Sight, The Limey, Sunset Boulevard, Nights of Cabiria, The Passion of Joan of Arc, Punishment Park, Raiders of the Lost Ark, Chungking Express

Actually, I'd probably be a lot more accurate if I went top 5 by genre, but I'll have to do that later... (That's going to take some time.)

The Usual Suspects
Casablanca
Memento
The Matrix
LA Confidential

Leon
Cinema Paradiso
Rushmore
Sleeper
When Harry Met Sally

1. 2001
2. Taxi Driver
3. Apocalypse Now
4. Raging Bull
5. Heat
5. Road Warrior
5. Days of Heaven
5. Blade Runner
5. Last of the Mohicans
5. Dersu Uzala
5. Brazil
5. Andrei Rublev

1. C'era una volta il West (Leone, 1968)
2. The Wild Bunch (Peckinpah, 1969)
3. Mulholland Dr. (Lynch, 2001)
4. The Deer Hunter (Cimino, 1978)
5. Modern Times (Chaplin, 1936)

City of God
Oldboy
Taxi Driver
Big Fish
Lord of War
-------------
Se7en
Into the Wild
No Country for Old Men
Brick
Happiness

Another Time Machine lover! This has been my favorite movie since I saw it as a kid in the early sixties.

2. On Her Majesty's Secret Service
3. Where Eagles Dare
4. Poseidon Adventure(1972)
5. Midnight Express

Brazil
The Godfather Part II
Jaws
GoodFellas
Fight Club

1) Somewhere In Time
2) The Untouchables
3) The Godfather
4) Star Trek II: The Wrath of Khan
5) Jaws

The Thing
Once Upon A Time In The West
Blue Velvet

The other 2 spots change so often it would be ridiculous for me to put anything in there.

Empire Strikes Back
Casablanca
The Matrix
Fight Club
Brotherhood of the Wolf

Drama:
Seven Samurai
The Big Sleep
The Petrified Forest
Goodfellas
El Cid

Science Fiction:
Forbidden Planet
Aliens
Star Trek II
Total Recall
The War of the Worlds (1952)

Westerns:
Open Range
Warlock
The Shootist
The Searchers
Winchester '73

Action/Adventure:
Die Hard
Dr. No
Raiders of the Lost Ark
Licence to Kill
Die Hard 2

The Good, the Bad and the Ugly (Sergio Leone)
The Wild Bunch (Sam Peckinpah)
The Birds (Alfred Hitchcock) - not his best, but my personal favorite
Citizen Kane (Orson Welles) - obvious choice, but it's just that great
Beyond the Valley of the Dolls (Russ Meyer)

The Apartment (Billy Wilder)
The Big Sleep (Howard Hawks)
The 7th Victim (Mark Robson)
Miller's Crossing (Joel and Ethan Coen)
Blue Velvet (David Lynch)

I watch these the most:

1. Goodfellas
2. Pulp Fiction
3. The Boondock Saints
4. The Blues Brothers
5. Fight Club
6. The Godfather
7. Fargo
8. Office Space
9. Dazed & Confused
10. Rounders

1.Pulp Fiction
2.Empire Strikes Back
3.Fellowship of the ring
4.Kill Bill
5.Clerks

I like your idea.

Just favorites, not what I consider the best:

Sci-Fi:
Star Wars (Original Trilogy)
2001
Blade Runner
Sunshine
Close Encounters of the Third Kind


Horror:
A L I E N
The Thing
Dawn of the Dead (Original)
Halloween (Original)
Texas Chainsaw Massacre (Original)


Drama:
Godfather 2
No Country for Old Men
Clockwork Orange
25th Hour
Taxi Driver


Comedy:
Fear and Loathing in Las Vegas
Dazed & Confused
Big Lebowski
Rules of Attraction
Super Troopers


Fantasy:
Excalibur
Conan the Barbarian
Legend
Fellowship of the Ring
Return of the King


War/History:
Patton
Apocalypse Now
Das Boot
The Right Stuff
Kingdom of Heaven


Suspense/Thriller:
Se7en
Silence of The Lambs
Zodiac
Dead Ringers
The Shining


Western:
Unforgiven
The Good, The Bad, & The Ugly
Once Upon a Time in the West
The Wild Bunch
The Proposition


Action/Adventure:
Raiders of the Lost Ark
Road Warrior
Escape From New York
Predator
Commando (Cheesy goodness!)


Foreign:
City Of God
Seven Samurai
Brotherhood of the Wolf
Downfall
Samurai Banners


Animated:
Ghost in The Shell
Akira
Steamboy
Toy Story
Lion King

Drama
1. Forrest Gump
2. E.T. The Extraterrestrial
3. Field of Dreams
4. JFK
5. Shawshank Redemption

Action/Thriller
1. Face/Off
2. Spartan
3. True Lies
4. The Rock
5. Speed

Comedy
1. Caddyshack
2. Animal House
3. Blues Brothers
4. Snatch
5. The Girl Next Door(Elisha Cuthbert)

Western
1. Buono, il brutto, il cattivo, Il
2. 3:10 to Yuma(07)
3. Unforgiven
4. Tombstone
5. Wyatt Earp

War
1. Saving Private Ryan
2. Patton
3. Lawrence of Arabia
4. Black Hawk Down
5. Kingdom of Heaven Directors Cut

Horror
1. The Exorcist
2. Silence of the Lambs
3. Halloween
4. Saw
5. Feast(Gloriously over the top; the first half hour is hysterically funny)

Braveheart
Almost Famous
Star Wars
the Shawshank Redemption
the Crow