UPDATE: I can't be bothered adding links for every mod except the main mods I always use and have already added links to. The names should be enough to find the rest.
This is something of a breakdown of the mods I like and particularly recommend. Where there are addons I use for various mods I'll add them with the mod description.
Some will be mods I've used and loved in the past but for various reasons have moved onto others. My tastes in weapon and armour mods changes like the wind except for a very select few. There are mods I wouldn't even consider playing without, so they will get a mention first after the main tools and utilities I use.
Essential tools and Utilities:
Wrye Bash, Oblivion Mod Manager, B.O.S.S. (Better Oblivion Sorting Software), TES4Edit and/or TES4Gecko and TES4LODGen. These are the exact names so they are all easy to find without linking every one.
If I had to choose only one mod from my very large load order it would be Waalx Animals and Creatures which can be found here: Registration is required to view and download the file but there is an open screen shot thread to give any idea of what it adds.http://waalx.com/RealSwordsForum/index.php
This mod adds more than what the title alone suggests. It creates the kind of world I envisage as a true medieval experience along with of course the awesome animals and creatures. If you know of the Realswords series, it is made by the same author, Waalx, and those mods are integrated as well as a lot of armour and clothing suited to the era.
Take no notice of the Beta status. The mod is extremely stable and has caused me no problems whatsoever.
Since I use HGEC as a female body replacer there is also a conversion available at this blog which works perfectly.You will need to translate the page using Google or other translator, but the files work with any language version of the game as they are only meshes.
Now available at Tesnexus:
I used to use FCOM and OOO and MMM themselves are still dear to my Oblivion heart, but the time finally came when my computer started to protest and I felt the need of a change. My thanks to the people involved in those mods. You gave me many uncounted hours of enjoyment.
Next is Elsweyr the Deserts of Anequina which completes the entire province of Elsweyr in the tradition of the home of the Khajiit. This mod is a work of art and I spend more time there than in Cyrodiil. I love the desert landscapes and exotic locations. There are some very good quests as well.
Tesnexus link which leads to a mirror download. This mod is also very large as is WAC, but eminently worth the download many times over.
This site has a large selection of screen shots to get an idea of what the mod contains:
HGEC and Robert's Male body replacer patch for Elsweyr the Deserts of Anequina.
Reaper's Anequina Manor. A beautiful and detailed player home with a nice quest.
Maps of the Province are available and linked with the main mod description at Tesnexus as well as other addons of interest.
COBL (Common Oblivion)
Taken from the actual description this is a world enrichment mod adding lots of things that enhance the world without being intrusive.
Among many other things it adds The Luggage, a sentient chest that's featured in novels by one of my favourite authors, Terry Pratchett.
Adds apple and orange trees throughout Cyrodiil as well as the ability to harvest mushrooms from logs and feed horses with hay to heal them or just for ambience. This includes your own horse as well as other vanilla ones and there is a patch for Alienslof's beautiful horses. I don't use the patch though as I have WAC horses in my game. You can pick the fruit from the trees or use them as target practice. You can also harvest Nirnroots and flower bouquets which will regrow after three days.
I suppose Shivering Isles deserves a mention somewhere here since this list is so far taken from my load order, but I really only have it for the added functionality of the CS etc. I've never finished the main SI quest and always forget when I'm in game that it's even there. It's not that I don't like it, because I do, but it has a few of the annoyances the vanilla main game has and it puts me off. The main one of those is the ridiculous level scaling although I think the SI Main Quest is better than the Oblivion one. It's certainly more entertaining. Maybe I'll finish it one day.
I have the Knights of the Nine DVD but only tried it and the other DLC's once. There are far better user made mods than these and less buggy.
Next is All Natural. The ultimate in weather mods, which includes an updated version of Real Lights and Natural Interiors. To be continued....