I haven't seen anyone mention COBL yet, and I consider that essential personally, and definitely RP friendly.
Also Item Interchange helps with that (sorry no links right now, I'm in a rush
). I see you're planning to add Better Cities; good call!
I feel I should note that it doesn't touch the smaller settlements across cyrodiil, so you may want to get mods that improve them (I use AFK_Weye for example, and I believe somebody's currently working on a new Hackdirt or something like that).
Tamriel Travellers and/or a Crowded Roads mod make great additions to wandering the wilderness imho, and I wouldn't discourage using Crowded Cities or MoDem's City Life to spruce up your cities in the NPC department (note: MoDem's might conflict with Better Cities; I forget).
LAME and RBP were already mentioned, but I feel I should myself mention that I would have a very hard time playing without them.
The Ayleid Steps is a good install-it-and-forget-about-it mod.
If you want quest mods, I recommend The Lost Spires; it's one of a very, very few quest mods I always have installed.
I would also second Conduit Magic, although it can be overpowered at times (in that you can apply normal cast on touch spells to, say, a bow, and spam powerful ranged magic at half the cost or the like)
I enjoy Midas Magic - Spells of Aurum personally, although it also gives the player character an advantage over NPCs (I've never seen any of them summon a flying carpet, for example).
I would encourage you to grab all the Unique Landscape mods personally, as I feel they nicely improve the fun of wandering the wilderness of Oblivion.
Elys Uncapper and Legendary Abilities get rid of level/skill caps, which is nice, especially if you really want to make a specialized character who might pump some of his stats up past 100.
The Cyrodiil NPC Remodeling Project (CNRP) mods are great, and don't conflict with really anything.
Companion Share and Recruit is cool, although somewhat script heavy if I recall (I run it, but I don't utilize it often).
Grey Tide (or was it "Gray" Tide?) is my favorite PC home; a boat you can buy on the Waterfront Docks (doesn't conflict with BC)
Arena Alive is nice (more spectators in the arena, among other gameplay tweaks)
Streamline is great if your PC is struggling to run modded Oblivion.
Oblivion Crash Prevention System actually works, just so you know
Alternative Start Arrive By Ship is great in my opinion, in that you don't have to run through the sewers every time you make a new character.
Exnem's Runeskulls is another fun install-and-forget-about mod.
FormID Finder is pretty much essential for troubleshooting stuff, and nice to have in general.
Ambient Town Noises is great in my opinion.
~Visual Mods I Love~
A book cover mod, either Medieval Book Textures or Book Jackets + Book Jackets SI would be good.
Beaming Sunglare Replacer is SUCH an improvement; it's probably my favorite replacer mod. Every day-time screenie will look 13.76 times more awesome (scientific fact) with this
Rainbows in Tamriel is a nice touch (and doesn't conflict with other weather mods)
Finger Snap Animation Replacer is a nice touch for mages.
Better Silverware makes you actually want to collect silver urns and that crap because they're just so darned pretty :drool:
Glittering Prizes adds a sparkle effect to all gems and coins (looks really good with HDR imho)
Snow Texture Replacer is great.
...so is Visually Realistic Lava
Cathedral Improved Stained Glass is nice, although very vibrant, so it's up to your preference if you want overly-dull vanilla windows or overly-bright modded ones
Elven Map Redux is a nice looking map replacer.
oh, and if we're still discussing leveling mods, I use nGCD, but I haven't tested around a whole lot, so whatever
~Self-Plug Warning~ My mod Shivering Armour Variety makes me very happy inside, and I plan to keep dropping it's name until I realize nobody else is going to use it
~End of Warning~
Wow, that was a lot longer than I expected... hmm, I have spent way to much of my life doing this... and here's to many more years of it :foodndrink:
CC