[Tokolosh]

You can't go wrong with Kurosawa. Get them all if possible.
Same goes for Sam Fullers films. One of my alltime favorite directors.

Also:
The Third Man - Carol Reed
The Spirit of the Beehive - Victor Erice (Spanish cinema at it's best)
Lars von Trier's The Element of Crime and Europa are must haves in my book.
The list goes on and on...

Oh, and Salo is NOT overrated as some may say. It's a masterpiece, zots.