Apart from the quest that nets you the two rings, as well as the quest that nets you the two amulets, which other side quests offer permanent, unique rewards? These are getting very repetitive, and I'd like some advice on which quests are arguably the, "must do for the rewards" quests.

I guess that all depends on what you would consider a "must do" or "must have". For me, my "must have" in those side quests was The Gift quest. The ability to turn my spouse into a vampire that doesn't have any of the bat-face changes that make the newer vampires so butt ugly. That's the only way in the game to do that, so for me that was a "must have". As for the other side quests I can't really say because I haven't finished more than 2 of them, but the ones I've heard of so far seem pretty skippable to me.

I enjoyed The Gift as well.