Carsomyr

Carsomyr, The Holy Avenger is a holy two handed sword which can only be used by paladins and it's class kits.. This sword can be obtained if the dragon Firkraag, who can be found in the ruins of Windspear Hills is killed. The party obtains the +5 version of this weapon in Baldur's Gate II: Shadows of Amn. Cespenar, who is found in Baldur's Gate II: Throne of Bhaal, can upgrade this weapon to it's +6 version if the party is willing to use the Eye of Tyr.

Carsomyr +5
Carsomyr +5 offers the wielder a 50% magic resistance, allows the user to use dispel magic thrice per day, dispels conjured weapons every time it hits and does +5 damage to creatures of chaotic evil alignment. The two handed sword inflicts 1d12 +5 damage, has +5 thaco

In-game description
"Carsomyr is a weapon of legend, perhaps one of the most powerful blades ever forged on Faerun, though its origin and history is thought purposefully forgotten, such that the sword itself never overshadow the importance of the struggles that must be fought today. It is infused with the very essence of virtue, and requires as much from any paladin that would hope to wield it. The evils of the Realms must truly stand aside when this weapon is brought to bear, their magic dispelled with a word, steadfastly resisted with ease. Carsomyr also harbors a special distaste for the forces of evil and chaos, and such creatures must fear additional damage from its touch in battle."