All right,
excellent choices everyone!
I think that Luna has a point with The Thing, because it is a very unique movie in the way that it was shot, almost in a 'doumentary' style at times.
It gives the audience a deeper sense of fear through the fact that the story takes place in isolated Antarctica where the characters have no hope at all for rescue from the outside world.

Here is a pic of me in the morning.
(only kidding, it's a screenshot from The Thing)
Spaceballs, Spaceballs, Spaceballs.
A cult classic.
I wouldn't be surprised if one day they start having 'costume party' type showings at theaters the way they do with Rocky Horror Picture show.
Now this:

may not be the 'best' movie in my opinion but it is an example of what I call a
'Hollywood formula' movie, in that the content and cadence are edited to 'perfection'.
One scene flows seamlessly into the next, and the comedy and sight gags are well tuned and timed instruments unto themselves.