http://en.wikipedia.org/wiki/Blade_Runner
http://www.amazon.com/gp/richpub/syltguides/fullview/R2VT2ECILZ4O3B
The 5 versions are:-
1) original cinema release International version. This has the cheesy voiceover and tacked on happy ending (oddly an unused scene from the Shining).
2) original cinema release for the US market which was like the Internmational version only with a few minor edits of the more gory bits.
3) Directors Cut - no voiceover, no happy ending and the inclusion of the infamous Unicorn scene. A much better film in many ways although I have great affection for the original version. Still apparently not the film Scott wanted to make because for some reason he didn't oversee the actual editing of this version directly.
4) Workprint version which was apparently a quite radically edited version of the film with various changes including an altered opening scene, no Deckard narration until the final scenes, no "unicorn" sequence, no Deckard/Rachel "happy ending," altered lines between Batty (Rutger Hauer) and his creator Tyrell (Joe Turkell), alternate music etc. Like most people I have never seen this version.
5) The film Scott wanted to make in the first place apparently. Not sure exactly what changes have been made except it is a bit longer which suggests a few scenes have been added or extended. It has been digitally remastered and surround sound added. And some of the effects have been cleaned up.