weather: all natural
enhanced weather (weathers from this mod are used in Weather: All Natural, but enhanced weather itself is not bundled)
enhanced water
enhanced vegetation
detailed terrain
vibrant textures by CorePC
Bomret's detailed normals
beaming sunglare
those are what i use, anyway. i also use a pop-up grass retexture to match the ground better, but forgot the name.
also, don't forget to use PyFFI, Operation Optimization, and Low Poly Grass for better fps
edit: QTP3R is nice, too, but I only use the clutter and furniture etc from it. Oblivion Stutter Remover is pretty much essential, and Streamline's Streamsight feature helps with fps and immersion. which reminds me of RAEVWD (Really Almost Everything Viewable When Distant) which you have to be careful with as it can cripple fps. and there's also animated windows and smoking chimneys.