With the debug mode enabled, press CTRL+Space to open the console window. Enter: CLUAConsole:CreateItem("killsw01"), then press .
This will create a weapon which is listed as a Longsword +2: Varscona. But this weapon does about 1000 damage, gives a massive bonus to AC and THAC0. Also, it can be dual-wielded and the AC bonus does stack. It can be used by any character, regardless of class or proficiencies. It also gives 100% magic resistance and Improved Haste.
Baldur's Gate II: Shadows of AmnAdded 18 Mar 2005, ID #6046
Best Sword Ever: To get a +2 sword enter the code killsw02 and once equipped it does 1000 damage a hit and puts your armor class down 10 and will also give special powers like haste and magic resistance.