S.T.A.L.K.E.R.: Shadow of Chernobyl
Patches
Patch is currently at version 1.0005. It is heavily recommended to patch to the latest version.
Complete Mod 2012
It is also recommended to download the Complete Mod. It contains major bug fixes, A.I improvements, upgraded shaders, new higher resolution textures, sounds, music, weather and visual effects. Without hindering the feel of the original game, so it can also be used by new players.
Zone Reclamation Project (1.7 XR2)
A bug fix mod that tries to keep the game as vanilla as possible, or not depending on how you set it up.