Nexus Mod Manager
http://www.skyrimnexus.com/content/modmanager/
If you don't already know about this, it's a mod manager that works with Skyrim, Oblivion, Fallout 3, and I think some other games. It will make managing your mods easier. Also allows you to download directly to it from Skyrim Nexus.
Tytanis-The Ultimate Mod
http://www.skyrimnexus.com/downloads/file.php?id=1601
This mod does a ton to list it all. Some highlights include being able to craft armor like Nightingale Armor, Blade Armor, Dragonbone weapons (retextured Orcish weapons), smelt items into raw materials, I still haven't looked at all it can do.
Nightingale Prime Armor
http://www.skyrimnexus.com/downloads/file.php?id=1896
Retexture of the Nightingale Armor. Haven't actually seen used it myself but the screenshots look good.
Deadly Serious Shrouded Armor
http://www.skyrimnexus.com/downloads/file.php?id=2260
Retexture of the Shrouded Armor. I LOVE this as it makes it look so much better. The hood is changed. It looks like a priest's hood with a cape coming down from it. Personally, I didn't really like it that much. If you don't want to use it, download it manually and delete all the hood files in the textures and meshes folders.
QD Inventory
http://www.skyrimnexus.com/downloads/file.php?id=667
Changes the Items layout so it's much better.
No More Blocky Faces by Xenius
http://www.skyrimnexus.com/downloads/file.php?id=30
As it says, no more blocky faces. Makes characters look a lot better. May be required by some other mods.
Detailed Faces v2 by Xenius
http://www.skyrimnexus.com/downloads/file.php?id=26
Detailed faces. Works with No More Blocky Faces (same creator).
For more character enhancement mods by this creator, check here:
http://www.skyrimnexus.com/downloads/file.php?id=2356
Better Females by Bella
http://www.skyrimnexus.com/downloads/file.php?id=2812
It's gotten a lot of endorsements, but I didn't like it. While it's great if you're creating a female character to play, it just doesn't look that good on NPCs. The creator did add a more basic version which just improves textures (requires No More Blocky Faces) but I've not had the chance to see it myself.
Glowing Ore Veins 300
http://www.skyrimnexus.com/downloads/file.php?id=193
Ore veins glow so they're easier to see.
Non-Playable Armor
http://www.skyrimnexus.com/downloads/file.php?id=820
Allows you to obtain the locked armor/clothing NPCs wear. Some examples include the Tortuer's Hood (guy you encounter when you escape Helgen) and Nocturnal's Robes (giggity).