So I'm probably going to get the PC version of the game in a week or so, and I should have a good enough machine to max everything and use higher res textures as well. What are some must have mods? I know that's been asked plenty in here, but I wouldn't know how out of date any of the suggestions are.
Skyboost (or whatever it's called now) is a must. Improves performance for everyone. Then again, it's possible the 1.4 patch implements the optimizations of Skyboost, so it may become unnecessary (like the 1.2 patch did with LAA).
SkyUI is great for sorting. I never really used the default UI but I've seen it on the Xbox version, and SkyUI is a pretty solid improvement. There are a few different map improvements; I use one called Realisitic Map with Roads, which mimics the look of the original map, but adds in all the roads so you can figure out just how you're supposed to climb a cliff or what have you.
As far as texture mods, I really like the XCE (Xenius Character Enhancement) pack. It's a series of mods that address the major issue of crappy player models without much of a performance hit. I added Hi-Res packs for NPC Clothing and Armor, because it's silly seeing a high-res character model in a low-res outfit, but those texture packs can get pretty big (over 1 GB for the HD armor).
I like Realistic Water Textures by isoku and the Enhanced Night mod which adds a ton of stars and a colorful galaxy. Both of these offer better immersion for basically no performance hit. Same with Improved Dust Particles; basically no change to performance, but the game looks way better for it.
Glowing Ore Veins is a great mod provided you don't consider it cheating to be able to spot ore veins from half a mile away. Useful, but I could understand why some people wouldn't want it.
The Skyrim Flora overhaul is highly recommended by lots of people, but honestly, I don't see that big a difference when using it, other than a massive hit to performance in certain areas (outside Riften drops from a solid 60 to 48). If you've got the rig for it, it does look better, but for most people, the performance decrease isn't worth it.
There's also some mods that improve your housing situation; one adds a full smithing area to the basement of your house in Solitude (forgot the name of that one), and the Dohvakin Hideout adds a large basement with connections to all the houses you can buy (haven't tried this one, seems a little ridiculous to have warps to all your houses).
You might look into the crafting mods. Being able to make arrows is a pretty important thing if you're an archer. Reweighed Potions makes it easier to roll into battle without potions taking up 50 pounds of inventory. There are lots of mods that add new craftables like new weapons or jewlery, but I haven't tried any, so I can't recommend them.
I'd say the absolute must-have mods to start with are Skyboost, SkyUI, Realistic Water Textures, Improved Night Sky, Improved Dust Particles, Xenius Character Enhancement and Glowing Ore Veins. If you've got the system power, definitely get the HD NPC Clothing and HD Armor mods. The other stuff is more about how you want the game to play; these mods will make the game look a lot better.
Oh, and the Nexus Mod Manager is a pretty good way to keep everything sorted and up to date.
This thread at NeoGaf has some great information and examples of lots of different mods, including all the ones I mentioned.