Depending on which ones you haven't seen, how have you not seen some of this stuff? It's pretty hard to pick just five. I would recommend some stuff just because it's pretty well-known everywhere and culturally significant, not because I necessarily like it (e.g. Star Wars).
Watch:
Pulp Fiction
Lion King
Back to the Future
Shawshank Redemption
12 Angry Men
Skip:
Forgeting Sarah Marshall
Matrix Revolutions
Harry Potter and the Sorceror's Stone
One Flew over the Cuckoo's Nest
(books are better for the last two)
I'd say most of the list is definitely worth watching.