I have quite a few, and I've tweaked them such that they all work together flawlessly (up until today):
DarkUId DarN
Oblivion Character Overhaul
Open Cities
Better Dungeons
Knights of the Nine
Shivering Isles
Illumination Within Windows/Lights
Loading Screens (for DarN)
Natural Water
Natural Weather
Brighter Torches
Enhanced Vegetation
Archers Lodge
PTFallingStars
Adventurers Guides (books with commands)
any armor (allows you to wear other armors in Arena)
Better Camps (adds fire places etc to camps)
Bow Damage Equalizer
Dangerous Wilderness
Deadlier Sneaking
Demonocus-grey prince chest of gold
Fast Travel Expanded
Faster Arrows 225
Grab Power
Healthy Gear (increases durability of items)
KT Vamp sight toggle (hunters sight toggle instead of timed)
Lights (toggleable candles etc--doesnt' work most of the time...)
Master of Athletics Ability (allows you to run on water--also doesn't really work)
Oblivifall - Something's Not Right (adds captions when you're near a dungeon of sorts that say things like "You notice spiders scuttle across the path" or "Horses have passed this way recently")
Prox - Arena Loot
Quest Award Leveling -Finger of the Mountain and regular
Remove Trainer Bounds (train 500 times per level instead of 5)
See U dead (removes forced reload on death)
SoT's Rings (adds a bunch of cheat rings)
Toggleable Quantity Prompt (pressing shift will pick up all of an item, ctrl will pick up one)
TrainerFind (spell that points you toward trainers)
Tropical Island
Unlimited Weapon Recharge (Varla Stone that recharges your gear when it runs out)
Weightless Ingredients
WPHealthRegen (out of combat health regeneration)
Adventurer's Spells (Mark, Recall, etc)
Harvest Flora
Waterfront shack overhaul
Natural Rings Limit