These posters represent a remarkable and relatively unknown art form that deserves some recognition. Rather than simply slapping together a movie still and some text (obviously I'm generalizing here), these artists produced something that can be considered a work of art in its own right. Playful and often moving, some of the trademarks of these posters include a dynamic style, bright colors and unusual compositions. Each artist has their own unique style, which is what makes these posters so special.
The prices, for the most part, are pretty reasonable as well.
The best resource on the web seems to be PolishPoster.com...if anyone's interested I will report back once my purchase goes through.
Some of my current favorites:
La Village Magique, by Jan Mlodozeniec
Gra, by Jan Mlodozeniec
Parasol, by Franciszek Starowieyski
Iwan Grozny, by Franciszek Starowieyski
Kobiety by Maria Ihnatowicz
Stories About Lenin, by Jan Lenica
Desire, by Jerzy Flisak
My all time favorite is this superfantastic Arcimbaldo-esque Casanova: Childhood and Adolescence poster by Marek Mosinski... which will hopefully be up in my apartment very soon.