Night Vendors adds several new vendors that sleep by day and sell at night. The NPCs are mostly immigrants from Morrowind that are used to being able to get services any time of day or night. They don't have that much money and they don't sell any uber items. You can expect to find some ammo, ingredients, a few potions, repair hammers, etc. They are just like normal people in that they still don't like vampires, even though they sell at night.
Each NPC has their own schedule. They are convenient for when you get into town at 6:30 pm and want to stock up on arrows, but you don't want to wait around until morning. If you use my http://planetelderscrolls.gamespy.com/View.php?view=OblivionMods.Detail&id=4987 mod these vendors will also sell the new potions, but it is not required.
Currently adds merchants to the following places:
Bravil - Mages Guild
Bruma - Chapel
Cheydinhal - Newlands Lodge
Chorrol - Mages Guild
Leyawiin - Fighters Guild
I plan on adding at least one to every city. Download http://planetelderscrolls.gamespy.com/View.php?view=OblivionMods.Detail&id=6420.