...Or you could just ask me
IMO, I think Shadowrend is the best "Hidden" weapon. But it's in Shivering Isles. So if you don't have that don't worry about it.
shadow rend is definately the best weapon in the game, and is almost always over looked. i know pretty much everything about oblivion, to get shadowrend, do the main quest for shivering isles and when your building your staff, you have to go to a tree and fight a shadow version of yourself. be sure to search its body because its carrying shadowrend.