Always one of my favourite questions, but because I am awkward, I have to split it into two catagories. One for stuff I love to watch regardless of my mood, and two, for those which I can watch because they are great examples of the power of film...so here goes!
-American Graffiti
-GhostBusters
-Rushmore
-Seven Brides for Seven Brothers (good pick Michelle, surprised I like it?)
-Evil Dead II
-Donnie Darko
-Groundhog Day
-Star Wars 1-6
-Goodfellas
The for catagory two there is stuff like Texas Chainsaw Massacre (original of course), Fight Club, Robocop, Suspiria, Living Dead at Manchester Morgue, Taxi Driver, Scarface, Magnolia, The Exorcist, Videodrome....
Honestly, I could go on, but I will have mercy!