The Sith Lords Restored Content Mod (TSLRCM)
The TSLRCM is a hugely substantial mod that helps the game meet the vision that Obsidian had originally planned for the game. Not only does the mod fix a whole host of bugs, including broken items, dialogue tree errors and combat glitches, it has pulled content out of the code and made entire areas of the game playable including unusued audio files and dialogue trees. The most recent build has also introduced compatibility with the long-awaited M4-78 Enhancement Project, aka Droid Planet.
To install TSLRCM:
1) Download and install the mod from the official ModDB entry, now at version 1.18.2.
2) Make sure to install the mod at the correct Steam location, where the default location is here: C:\Program Files (x86)\Steam\steamapps\common\Knights of the Old Republic II\ (unlike other KOTOR2 mods which fit into the \Overide\ folder).
3) Ensure that the Steam doesn’t accidentally overwrite the mod by disabling updates to the game (Right click on KOTOR2 in the library > Properties > Updates tab > Do not automatically update this game).
4) Mod installation is confirmed if the main menu of the game shows The Sith Lords Restored Content Mod 1.8.1.