The Unofficial Oblivion Patch from Best Oblivion Mods
It's the first thing that should be downloaded out of all essential Oblivion mods. This unofficial patch is the result of community's combined efforts to fix bugs found in the base game. Currently, it puts an end to over 2,300 bugs and 70,000 object placement errors! Lots of minor and major improvements are included to make your experience more pleasant.