There is also a Finnish indie movie based on (or inspired by) it, called Vyöhyke (the zone) [1]. Nowhere near as good as Stalker, but it was published on Youtube [2], so it's easy&free to watch if you have the time to spare.

[1] http://www.imdb.com/title/tt2627842/

[2] http://youtube.com/watch?v=EwkIaJX3hmg