There are a lot of good assassin armors out there to be sure, unfotunatly most of them come as a replacer for the DB shrouded armor. Now I am not to fond of the vanilla shrouded armor myself, but this creates the problem that you can only ever have one of these armor set installed at once.
I've been thinking that it would really be something if someone were to colaborate with the mod authors of the replacers mods and make a collection of each of the armor set as a nonreplacer armor, but its own stand alone set. In the end that would add like 5 or 6 new set of assassin styled armor to the game. You could even have each member of the Dark Brotherhood be wearing a diffferent kind of armor making them each seem a little more unque.
I am sure this mod would not be terribly difficult to do, assuming the original mod authors are willing to get on board.