A khajiit NPC named Rasqaar is added onto the lower level of the dawnstar sancutary upon completion of the dark brotherhood quest line. He sells the followng:

- Shrouded assassin armour
- A new weapon named Assassins Katana
- Shrouded assassin robes
- A bunch of leveled weapons and common alchemical ingredients
- A handful of gems
- Shrouded worn assassin armour

If you are using the UFO mod, the extra assassin armour and weapons come in handy for you to re outfit all of your companions untill you have a small company of followers that will look the part of an assassin, fun to ransack cities with :)

Adittedly this only a small mod but I felt that just having babette selling mostly alchemical supplies wasn't enough barter for the end of the questline and I thought being able to buy new sets of assassin armour for your companions would be cool. I am still learning the ropes in the creation kit, but please express your opinion in the comments.

If you download this mod before completion of the dark brotherhood, then you will not find rasqaar in the sanctuary, instead he stays in the abandoned shack untill you finish the questline and you will also be unable to barter with him untill he enters the new sanctuary.

My other mods:
Mercenary Company: http://skyrim.nexusmods.com/mods/29560