This is everything I'm using - a lot of textures, meshes, lighting, flora, better females with more hairstyles, tweaks. I want to keep the vanilla gameplay and enhance it. No major changes, no excessive colors, armors, etc. Only one mod that really changes gameplay, thats the bags mod which I haven't tried yet. You're welcome to recommend other mods.

I'm using i5 2500k 4GHz with GTX 670 SLI - with adaptive vsync and ugridstoload=7 fps is 40-60, minimal stutter, smooth turning.

Also get these mods from nexus, really add a lot to the experience:

Project ENB - http://www.nexusmods.com/skyrim/mods/20781/ - I'm using realistic version, chose this ENB because it can be used with the next mod.
Climates Of Tamriel - http://www.nexusmods.com/skyrim/mods/17802/
Skyrim HD 2K Textures - http://www.nexusmods.com/skyrim/mods/607/ - Download 2K if you have up to 2GB VRAM. 4K if you have more than that. The difference is minimal to none if you don't look for it.
Project Parallax Remastered - http://www.nexusmods.com/skyrim/mods/40512/ - Download 1.3 HD2K if you have the previous mod, independent of resolution.
Realistic Lighting Overhaul - http://www.nexusmods.com/skyrim/mods/30450/ - Don't install any modules from COT and don't install weather module from RLO.
Apachii Skyhair - http://www.nexusmods.com/skyrim/mods/10168/
High Quality 3D Map - http://www.nexusmods.com/skyrim/mods/4817/ - Download only meshes if you plan on getting the next mod
A Quality World Map - http://www.nexusmods.com/skyrim/mods/4929/ - Download High-res quality all roads version if you have the previous mod.
Book Covers Skyrim - http://www.nexusmods.com/skyrim/mods/35399/ - Download 2.6.4 if you don't have DLC.

Advanced ini tweaks:
http://www.nexusmods.com/skyrim/articles/1153/ - performance tweaks
http://www.geforce.com/whats-new/guides/the-elder-scrolls-v-skyrim-tweak-guide#1 - very detailed guide with images

Update 1: added Ponytail hairstyles
Update 2: added Amazing follower tweaks
Update 3: added link to Apachii Skyhair, High Quality 3D Map, A Quality World Map and Book Covers Skyrim
Update 4: added Rainbows and Distant detail
Update 5: added Skyrim Enhanced theme
Update 6: added Footprints, added link to Realistic Lighting Overhaul, added notes and console commands
Update 7: added Enhanced Cities: Morthal 2.0, Enhanced Skyrim: High Hrothgar, Enhanced Cities: Docks of Solitude, Enhanced Cities: Jarl's House
Update 8: replaced Real Glaciers V2 with Real Glaciers Remastered

Notes:
If interior/exterior lighting is too dark/bright, I recommend modifying AmbientLightingIntensity lines in enbseries.ini. Shift+Enter if you want to modify them in-game and see the result, but you have to write them in the ini file after you exit the game.

Console commands:
refreshini - reload the skyrim ini files
tfc - free camera
tm - hides ui and pauses for taking screenshots
showracemenu - customize your character, useful if you want to change the hair