September 14, 2014 4:44 PM EDT
SKSE (duh), Frostfall, RND, SkyUI, iHUD, Wet and Cold, Immersive Armors, Dual Sheath Redux, Duel Combat Realism v5, Winter is coming - Cloaks, the Unofficial Patches. These are the most important mods for me. I could also mention the recently taken down Climate Overhaul - Winter mod. Paired with Frostfall it makes Skyrim an even harsher place, and since it completely changes the areas that weren't covered in snow before, it makes Skyrim feel fresh. Oh, and due to the amount of times I've been killmoved at high difficulties Violens has became an essential mod for me (you can finally toggle Player killmove immunity).
As for graphical mods I love Kinematic Enb and ELFX combined (interior module only), and also most of the popular high-res retexture mods (Skyrim 2K, Amidianborn, SMIM etc.)