Super Troopers
For repeated viewings, nothing matches it
And yea - Tombstone rules, Kurt Russel's second best picture behind The Thing(the original), and his third best, Big Trouble in Little China - the check is in the mail.
Memento just makes your head hurt.
Since Once Upon a Time in the West was mentioned, I'll mention the rest of the best of Sergio Leone: A Fistful of Dollars, For a Few More Dollars, and The Good, the Bad, and the Ugly - a great loosely connected trilogy that helped define the "Spaghetti" western. Once Upon a Time in America, while incredibly long(4 1/2 hours original cut), defined the modern gangster movie and is excellent.
Equililbrium is a great B-movie - similar to Orwell's 1984 starring an early Christian Bale and has Sean Bean
Some classics everyone should see:
Casablanca - The best of Bogart
Seven Samurai - Foreign classic, required watching
Dr Strangelove - Kubrick's(of A Clockwork Orange, etc) only comedy, excellent
Citizen Kane - Rosebud
Lawrence of Arabia - An epic biopic about T.E. Lawrence with a interesting bit of middle eastern history in the WWI era
Metropolis - A 1927 silent movie set in the distance future with androids and revolution - helped inspire the movie Blade Runner
Cool Hand Luke - Probably my most favorite movie of the 60s with Paul Newman, everyone knows the "What we have here is failure to communicate"
One Flew over the Cuckoo's Nest - Kesey may have hated the film version but it none the less excellent and excruciatingly depressing
Dog Day Afternoon - Based on a true story of a bank robbery in order to pay for a lame man's sex change starring an early Al Pacino
Chinatown - Roman Polanski's most famous, tho anything from Polanski is typically excellent
Ice Station Zebra - About recovering a film canister from one of the Keyhole satellites, really not good but I can't help but watch it - blame Howard Hughes
B Horror Movies:
Evil Dead, Evil Dead 2, Army of Darkness - Evil Dead 2 being the best imho
Dead Alive - Incredibly cheese gore zombie movies, definitely has some scenes that will upset some, Peter Jackson.
Meet the Feebles - Imagine the Muppets on crack and prostituting themselves - another early Peter Jackson of LoTR fame
The Story of Riki-Oh - What my avatar is from, super cheese gore, makes no sense, makes me want to learn to play the leaf
If you're not of the faint of heart, anything from Takashi Miike, king of Japanese shock horror, just beware he's made stuff that'll make your average 4chan user throw up
Classic WW2:
Midway - Story of the Battle of Midway starting Heston and Fonda
Patton - The story of America's most insane modern general
The Dirty Dozen - About taking men from the brig for a one-way secret mission in France during D-Day
A Bridge to Far - About Market Garden, Montgomery failed plan to end WW2 resulting in nothing good
The Desert Fox - A decent biopic about Rommel, master of tank warfare, attempted assassin of Hitler
The Great Escape - Steve McQueen, enough said.
Stalag 17 - American POWs held by the Nazis with escapes and betrayal
Kelly's Heros - Light hearted WW2 comedy
Recent war movies:
Band of Brothers: If you have watched this, do it now
The Pacific: Not as good as above but none-the-less excellent set in the pacific war of WW2
Defiance: Based on a true story of Jewish brothers escaping the Nazi's and living in the woods, rescuing over a thousand more jews
Schindler's List: Needs to be watched at least one time, after you're done and you've lost all hope for humanity watch the recent Louie CK interview on Conan about it and it'll cheer you up
Downfall: Watch Hitler's final days in his bunker, was well made fun of/sampled from on the internet after it came out
Black Hawk Down: See Delta Force, the 75th Rangers, and the 160th Nightstalkers in what is supposed to be one of the more accurate portrayal of modern war, very little character building
The Pianist: Roman Polaski again, be prepared to be depressed
Das Boot: Geman movie about the crew of a u-boat - by far the best submarine based war movie
Saints of Soldiers: About survivors after the Malmedy Massacre
Platoon: Vietnam, all star cast including Willem Dafoe, can't go wrong.
The Hunt for Red October: Tom Clancy novel, one of my favorites
Good Morning Vietnam: My favorite of Robin Williams
Rescue Dawn: Based on a true story, Vietnam POW, directed by Herzog, starring Christian Bale
Left out the more famous recent ones like Saving Private Ryan
Alright, I'm done...