Okay, here's a chance to make alists.
Movies that you must see twice because the first time you see them you either don't understand what the fuck is going on or you didn't appreciate it fully. And by 'didn't appreciate' I mean they are too complex or stuffed with info and interest that you can't take it all in in one sitting - NOT movies that you just think are cool so you watch more than once.

My list would be;

Spanish Prisoner - every time I see it I notice something new and small
Fight Club - the cinematography
Mulholland Drive - I can assure you the first time I saw this movie I just sat up and said "what the fuck?". Actually, I said what the fuck a lot of times during the final third of the movie.

the sixth sence-its a whole different movie when you know the twist

and for those who hadn't read the book when they saw the movie LOTR

I've seen The Fifth Element at least 50 times and I'm still picking up stuff from it.

I think Black Hawk Down would take some re-watching, totally confusing

The Matrix, when I can get a nice copied DVD, that is.

Or Dr Strangelove

Lost Highway (to get at least an idea of what it is about)
Naturtal Born Killers (for the insane amount of cuts)

Also Platoon

So far I agree with the Matrix, and haven't seen any of the other movies mentioned. :p

Matrix the second time isn't that good, except for the unbeatable acrionscenes of course.

I mean: follow the white rabbit, blablabla... it takes to long and they try to make it to complicated.

I say watch Trinity beat up cops, then skip to the blue/red pil scene.

naked gun 1,2&3

airplane 1&2

hotshots 1&2

loaded weapon

You always miss some jokes the first time. It have to watch 2 or 3 times to catch all the jokes.

Debbie does Dallas

Forrest Hump

Ally McSqueal

Naughty Naked Nurses 1-15........, uh.. wait, you mean mainstrean films, don't you.:o

Add misty rain's anal diary to your list :D