Well there's always Majesty, but in that game you play the god-like 'quest-giver' rather than the receiver. Hiring adventurers as you build up your city, and then sending them out on quests with promises of golden rewards!
Mount & Blade though might be right up your alley however. No plot to speak of, but the game is extremely open ended with insanely good combat and a surprisingly in-depth kingdom management system where you can swear loyalty to the leader of one of the various kingdom throughout the game, attempt to usurp a faction leader at the behest of a contender for the throne, or even try to create your own kingdom through invading and holding independent lands. One of my favorite games out there, and the mod community is extremely active as well.
Baldur's Gate 2 also had some management elements, and what was interesting is that it would change depending on what class you played in the game and was also entirely optional. Warriors could take control of a small keep and its surrounding lands. Cleric would be called in by their chosen temples to council disputes and play the mediator. Thieves could take control of a small guild. Druids could compete for control over a grove. Etc. Etc. Not quite as thorough or in-depth as NWN2's keep, but much more replayable since it was different each time.