Bullitt, best car chase ever!
Monsters (2010)
Very good movie. Its only time when it lets itself down that I can see is when it decides to show the creatures themselves, as Alien taught us it's always better to leave an element of ambiguity there when it comes to your creature.
Is that Thirst better than this Thirst? http://www.imdb.com/title/tt0762073/
As for me, Alien3, the most underrated movie of all time.
Paranormal Activity 2