Two essentials, for sure.

update -Top 5

The Toxic Avenger
The Crow
Bringing out the Dead
The Shawshank Redemption
Drop Dead Fred

Runners up

Love and a .45
Fargo
Pulp Fiction
Super Troopers
Romeo and Juliet (1968 version)

*probably over 25 movies could readily replace any of the runners up at any time :p
** probably movies I can't think of that even can replace some one or two of the top five

some more i thought of:

the good, the bad, and the ugly (don't know how i forgot this one)
straw dogs
brazil
the virgin spring
magnolia
pan's labyrinth
the graduate
adaptation.
pulp fiction
kids

what did you like about that film? i thought it was complete garbage.

whether or not you consider it a horror, I'm gonna put face/off on the list. Coz I'd call it more of an action.

its not horror at all.

If face-off is horror then Simpsons are horror too

I only said that because the idea of someones face being taken off and put on a psychopaths face is pretty bad. I'd class it as action but I thought there might be someone out there that classes it as horror.