I try to avoid adding dozens of random mods to my game, but there are some that I just can't live without.
DarNified UI. The UI was "designed" for console players and low-res TVs, and looks awful on a PC. This doesn't fix the control interface suckiness (like not being able to go directly to Potions etc) but it does make the HUD, world map, and all the menus much better than before.
Oblivion Gate Markers Mod (by UESP's own Robin Hood). The default game handles Oblivion Gates incredibly badly, especially considering they're one of the core elements of it. It doesn't put ones you've "seen" on the map until you get close enough to enter them - which would be fine if it used different icons for open and closed gates, but it doesn't. This adds quest markers to all the open Oblivion Gates that you've "seen" even if the map doesn't show them, so you can deal with them when you feel like it and you don't have to check 50 closed gates trying to find the ones that you haven't done yet.
Quest Award Leveller. I don't actually use many quest award items, but having to metagame them is just stupid.
Armory Lab. This is the "least bad" Basement mod I've found so far. The layout could be better, but the alchemy lab is excellent, and the armor display room is a big help for collectionistas like me.
Ali's Skeleton Key. Made all by myself (though it took me AGES). The lockpicking mini"game" sucks. It's annoyingly buggy, and by the time you've picked hundreds of locks it's beyond boring. If you have the Skeleton Key you can always open any lock, so I made it also add a Lesser Power that does an Open Very Hard Lock. It saves wasting HOURS over the course of the game waiting for the minigame to actually start working, and yawning through the pins or hammering the auto-attempt button, without having to grind Alteration all the way to 100. Oh, and it's On-TOUCH, unlike the "why on earth are these On-Target?!" normal Open spells, so it works underwater too. :D
I lost interest in Skyrim once the Shiny Newness wore off. The game is fun, but just so horribly buggy (and badly balanced). When Bethesda failed to release the CS for months and months, I decided I'd rather wait for some good mods to appear than keep playing it in the state it was in.
The Unofficial Skyrim Patch can't come soon enough. Until then though...
Weapons and Armor fixes. Quote: "955 Weapons out of 2,848, and 872 armors out of 2,762 are [bugged]". Or roughly 1 in every 3.
Ultimate Follower Overhaul. Doesn't fix the (non-)autoleveling bug, but at least lets you work around it without having to use console commands.
Shadow Striping Fix. Enough Said.
There's still a ton of stuff that's broken, and right now you need dozens of mods that each fix one bug (or at best one "set" of bugs, like Conjuration being utterly broken if you have the Atronach Stone), but there's a light at the end of the tunnel now.
Categorized Favorites Menu. Once again, Bethesda's UI is shockingly bad. This helps a lot, though it needs a plugin to be usable.
Better Females. Skyrim's inhabitants aren't the deformed mutants of Oblivion, but they've got broken Lego Faces and Bretons are especially horrific.
The Dance Of Death. Killcams are pretty. :)