A few that haven't been mentioned yet:
Letters from Iwo Jima, Fruitvale Station, Rush, The Impossibie, The Green Mile, The Mist, 12 Years A Slave, The Wild Bunch.

The Shinning
Pulp Fiction
Heros
The Prestige
Slumdog Millionaire
Stand by me
Taxi Driver
MUD
Blood Diamond
Kill Bill
The Hunt
The Terminator
Inside Man
L.A Confidential
Goodfellas
Man With No Name Trilogy
Once Upon A time in the west
American Beauty
The Silence of The Lambs
IP Man
The Goonies

Could List about 100 more, but i think ill stop here
also you could take a look at this http://www.imdb.com/chart/top

Silence of the Lambs is a must for any movie fan. If you want to watch the "sequels" skip Hannibal and go right to Red Dragon.

Gravity is one of the best recent movies and a great animated movie to watch is either Ratatouille (if you enjoy gastronomy) or Up.

Gravity
Captain Philips
Forest Gump
Cast Away
Saving Private Ryan
Catch me if you can
Se7en (or Seven)
Fight Club
Snatch
Gladiator
Shutter Island
Inception
The Departed
The man in the iron mask
Pirates of the Caribbean 1/2/3 (if you like those then watch 4)
Amadeus
City of God (this one is a brazilain movie, but holy fuck is it gooood!)
V for Vendetta (one of my favorite movies)

Comedy/ Animation

Megamind
Wreck it Ralph
How to train your dragon 1/2
Kung fu Panda 1/2
Chain of fools
Ace Ventura 1/2
Under Cover Brother (one of the best comedies i ever seen)
Kung Pow: Enter The Fist (the best comedy i ever seen)
Dude where's my car
21'st jump street
Superbad
Rolemodels
Airplane
Naked Gun
Anchorman
The whole 9 yards (these are fantastic movies, the first and the second)
The whole 10 yards
Pineapple express
Lion King (im dead serious!)

i want to thank all of you for all your recommendations. After reading all the suggestions i came to the conclusion that i've seen a lot of movies and more good ones than bad ones. Thankfully.

My last list of suggestions are:

Taking woodstock

Up in the air

Timecrimes

Brother

Limitless ( i thought this movie was a lot of fun )

Jacob's ladder

Citizen kane