And five more seeing as I'd decided on twenty, even if no-one is interested (some obvious but important ones here)
Hard to be a God
The Aleksei German version is a true cinematic masterpiece like nothing else I've ever seen - until I watched some of his earlier films which did lessen the effect slightly. Anyway this is the second or third adaptation of the Strugatsky brothers book but with a far less literal, much more dreamlike (actually nightmarish) feel to it that basically means that if you don't know the story you'll have no idea what's going on. No matter you just have to lie back and be pummelled into submission by the camera flying through the filth and horror and madness. It took years to make and German himself died just before it came out I think, as, possibly, did the surviving Strugatsky brother, having just time to watch it and give his seal of approval if I remember correctly.
Birds, Orphans, Fools,
I remember being intrigued by this after seeing Andy Votel (who is an expert in Czechoslovakian cinema) describing this as "possibly too weird". Honestly haven't seen it for years but I think it was kinda strange... with that childlike magical quality that I somehow always associate with a lot of these Czech things. Possibly (as Luka said) cos we had Svankmajer on telly all the time as kids.
Sweet Movie
Taboo busting musical(!) nastiness from the former Yugoslavia which was banned all around the world for years (and still is in some countries) and led to the ban on one of the actresses from returning to her own country. But it's not just for the sake of shock, there are many interesting ideas in there and it's got Pierre Clementi too - captured by Anna Planet in her boat filled with sweets and decorated with some guy's head...