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.
Enhanced Blood Textures - Better blood!
Enhanced Lights and FX - Creates a more dramatic mood by changing the lighting in certain areas.
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.
Get Snowy - Snow accumulates on your character if it's snowing.
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, which I'll suggest later...
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.
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.
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!
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.