Mages guild- an organization dedicated to studying legal forms of magic
This should propably be replaced with the Synod and College of Whispers. Not much is known about those more than what is mentioned in the book... And I have unfortuantely forgot what I read about them...
Necromancers guild-both a political and slightly criminal organization who backs up necromancy in all it's forms
Personally I hope one or both of the Guilds of Magic will allow necromancy in the guild and give them a more "good" viewpoint, not as anti-necromancers as we have been given before.
Fighters guild- hero's for hire who never break the law
Never break the law? I would say different guild chapters in different towns would be differently criminal, some being like the Blackwood Company. Quite dangerous, ruthless and illegal if those secrets sipped out. Others should be your ordinary good-guy warrior city guild chapter.
Vigilante guild- they work for something other than cash rewards and sometimes break the law for the greater good.
Something like an "we take the law in our own hands"-organisation? Sure, just expect it to have a few dirty secrets...
Thieves guild-a loosely organized guild of thieves and pickpockets.
The world just wouldnt be the same without these guys!
Imperial Guard organization- obviously we know what the guards stand for but it'd be cool to work your way up to captain
Aye, but the Empire propably should′nt have a very strong presence in town so make it more like joining the local mercenary group in the army, eventually maybe getting Knighted (and therefore not being in active duty) if you do some really big stuff.
Dark Brotherhood- Semi-honorable assasination organization with a lot of power and a lot of rules.
Skip the stupid rules here, I say. Just make them a "we got assasins, you want someone dead"-guild. Just business. And make them kill freelance assasins.
Vampire Coven-somewhat like the brotherhood but with hardly any rules but many rituals less organized and filled with vampires.
A few vampire clans wouldnt be so bad.
Progressives- down with slavery up with skooma, tolerance of differences, not quite as happy with the divines and accepting of deadric gods, social programs, down on war
Better split this up in different factions.
Conservatives- longs for the days of the old empire, less tolerant of change, religious when it comes to the 9 divines but no-tolerance for deadric gods, a strong imperial guard presence and pro-imperialism.
I would just call them the Imperial cult. Make them pro-imperialistic Imperials plotting for greater power to the Mede Empire.
Personally I would love seeing different Kingdoms and possibilities for you to become some part of the nobility there, getting yourself a estate, building a village, taxing your peasants, killing the insurgents, stealing their food and letting them starve in the mud... Hehehe... Just kidding!
But a bit like the Great Houses of Morrowind, but Kingdoms with more sovereignity to do stuff more openly...