My top 5 are:
Fight Club
Fave of all time, watched it when I was 12, changed my life
Taxi Driver
Film making doesn't get more real, honest and personal then this!
The Matrix
Again, changed the way I thought from a young age
Blade Runner
Deep, subtle and beautiful
Brazil
Hilarious/horrific, mesmerising/terrifying, beautiful/disgusting British sci-fi nightmare comedy
...and another five...
Blue Velvet
Surrealism in film at it's finest, flawless cinematic portrayal of corruption, sex and violence
Donnie Darko
Asks all the big questions about life, science and religion in a subtle and amazingly personal way
Seven
Morality, justice, evil- all masterfully presented themes in Fincher's beautifully horrible modern crime drama masterpiece!
Dekalog
Epic 10 part polish drama by Kiewslowski, the master of visual storytelling. Absolutely stunning
Spring, Summer, Autumn, Winter and spring
Had to put a Kim Ki Duk film in here, South Korea is on fire for film!