December 10, 2015 12:56 PM EST
The bloodskall blade? Requires the Dragonborn dlc but it looks sick and has a unique effect upon powerattacking that lets out a ranged beam. They're is also stormfang but its just a steel greatsword with the highest base damage I believe.
Edit: Just saw this post was made four years ago. Imma go dig a hole and throw myself in.