Better Torches - Increased brightness for torches, very handy if you've installed Climates of Tamriel or a similar darkness-increasing mod.
Bowlegged Jump Animation Fix - Changes the ugly "spread my legs" animation while jumping.
Clanking Armor - All armor no longer sounds like leather. Heavier armor now clanks when moving/running.
Cloaks of Skyrim - Cloaks! They look great, but they do tend to clip into other things (like your feet, sometimes weapons on your back, bolt quivers...).
Detailed Cities - Adds more objects to cities. Don't use if you're FPS starved.
Detailed Rugs - High-res rugs.
Dynavision - Dynamic Depth of Field without the use of an ENB. Highly customizable via MCM menu.
Enhanced Blood Textures - Better blood!
Enhanced Lights and FX - Creates a more dramatic mood by changing the lighting in certain areas. Install the optional SMIM meshes if you're using SMIM.
Enhanced Night Skyrim - Better nights! Changes the skybox at night to be clearer, shows galaxies and stars.
Expanded Winterhold Destruction Ruins - Winterhold sure doesn't look much like it was destroyed in a cataclysmic event. Now it does.
Follower Trap Safety - Because you can't really stop followers from triggering traps.
Frostfall - Hypothermia and freezing effects. Keep warm via fires, warmer climates, etc. I suggest using the Lite option for minimal tedium.
Get Snowy - Snow accumulates on your character if it's snowing.
Hectrol Caves Deluxe Highres Retex - Retexture of underground terrain. Adds a lot of missing detail to the vanilla caves.
Immediate Dragons - Dragons no longer require you to advance in the main quest to spawn. Best used if you're also downloading an alternate start mod.
Immersive Armors - More lore-friendly armors! Make sure to download the SkyRE compatibility patch if you're also downloading SkyRE.
Improved Combat Sounds - Better combat sounds!
Lanterns of Skyrim - All in One - Adds lanterns to cities, villages, roads, etc. Great if you're also using Climates of Tamriel, as the nights will be darker.
Lore-Based Loading Screens - Adds a few hundred loading screens with snippets from ES lore.
Main Menu Spinning Emblem - The Skyrim icon now spins!
Mercy - If someone begs for mercy, they actually stop fighting you. You can still kill them, of course.
No Skill Limit - Removes limits.
Populated Cities - Adds some generic townsfolk to the cities. They feel slightly out of place with names like Child or Veteran, but they sure help make cities more lively.
Random Alternate Start OR
Alternate Start - Live Another Life - Random Alternate Start spits you out randomly at one of a few hundred locations. Alternate Start - Live Another Life only gives you the option of spawning in a dozen or so locations (including the vanilla start), but you get to choose where.
Realistic Needs and Diseases - Gives a purpose to food. Player must eat, drink, and rest at regular intervals to stay healthy. I recommend turning down the rate at which you get tired, thirsty, and hungry by about half to minimize tedium.
Realistic Running Speed - Slows down running speeds by ~20% as well as matches NPCs running speeds to yours.
Ruins Clutter Improvement HD - Improves a lot of things you'll commonly see in dungeons and ruins. Also, 3d chain links!
SkyTEST - Enhances the AI for wildlife as well as adds predator/prey systems.
Static Mesh Improvement Mod - Similar to Ruins Clutter Improvement, but for everywhere else! Better models for all the little things in skyrim.
The Dance of Death - Adds more killmove animations. Also lets you tweak how often or not they trigger!
Thundering Shouts - Louder, deeper dragon shouts. RAWR I IZ DUVAKEN!
TK HitStop - Adds camera effects when striking an enemy. Customizable via MCM Menu.
Varied Guards and Stormcloaks - Changes up the gear that guards and stormcloaks wear. No longer are they all carbon copies of each other!
W.A.T.E.R - Improves water and everything to do with it. Better animations, better textures, etc.
Wet and Cold - Adds some dynamic effects for being wet/cold. Water will drip off you, you will breathe out warm, foggy air, etc.