Trying to avoid ones people have already picked...

6: The Day the Earth Stood Still
One of the finest movies of the 50's. Here's hoping the proposed remake falls through...

5: Bad Taste
Peter Jackson's debut, made for about $50. Aliens kidnap humans to sell in intergalactic fast food restaurants. Great fun.

4: The Adventures of Buckaroo Banzai Across the Eighth Dimension
Lots of aliens named John try to take over the world and only a brain surgeon rock star physicist can stop them.

3: Flash Gordon
Ming the Merciless wants to destroy the Earth because, you know, it's Tuesday. So far, only Dr Hans Zarkov (formerly of NASA) has offered any explanation...

2: Mars Attacks
I love the complete lack of motivation of the Martians.

1: Cloverfield
OK, I've not seen this one yet, but it looks very exciting. And the bad guys are probably aliens.