For now I'll mention just one mod, http://oblivion.nexusmods.com/mods/36966 by the creators of Companion Vilja. These beasts make perfect roleplay and immersionistic sense. What adventurer worth his or her salt would go off on extended foraging campaigns without a ready means to transport massive amounts of pillage? This in turn allows you to more realistically limit the amount of spoils your avatar can carry on his person without turning dungeon dives into non-profit endeavors. The donkeys (you can own more than one) have many functions and are highly configurable, making them more or less 'realistic' as you see fit.
Simple Portable Tent (http://oblivion.nexusmods.com/mods/41832)
Companion Fergus (http://oblivion.nexusmods.com/mods/37157)
Companion Vilja (http://oblivion.nexusmods.com/mods/28977)
The Elder Council (can't link for a number of reasons, but an 'expanded' version of the mod can be found here: http://oblivion.nexusmods.com/mods/22595)
Kvatch Rebuilt (http://oblivion.nexusmods.com/mods/15412)
I'll second the recommendation for a sophisticated companion, and Vilja is about as sophisticated as it gets, Oblivion wise. (I'm not familiar with Fergus.) The DC version of TEC sounds interesting. It looks to have made a least a few improvements to the non DC version I use. I like the COBL tie-in. Mine doesn't offer that. If and when I begin a new play-through I might consider switching to DC TEC. Then again, I'm pretty much sold on Kvatch Rising over Kvatch Rebulit. (I've used both. Rebuilt has the better reconstruction phases hands down, but I prefer the rebuilt city as it appears in Rising.) In any case either version of TEC, and a good Kvatch reconstruction mod, do indeed introduce otherwise unavailable roleplay opportunities.
I highly recommend http://oblivion.nexusmods.com/users/1006768 series of mods
Basic Primary Needs: Hunger/Thirst/Sleep
Ya know, I seriously debated adding a hunger/thirst/sleep mod for quite some time. In the end I didn't, for one very simple reason. If you follow my reports in our character update thread(s) you'll notice that my decrepit avatar eats and sleeps when and as he should, barring exceptional circumstances. That being the case, I don't really need a mod to goad me into doing so. On the other hand, I don't have the sort of imagination that would allow my avatar to do things on his own without some sort of official vanilla or mod-added assignment given by an NPC or other trigger. I therefore depend heavily on 'quest' mods.
-Decrepit-