Most of my mods are various weapons/armor, followers, races, a few homes and a couple of quests and dungeons.
The mods I absolutely can't live without, however, are:
Jump Higher: Because the vanilla jumping sucks and this mods makes getting around a lot easier.
Easy Lift Bodies and Objects: Because what's the point of killing people if you can't desecrate the corpses in hilarious ways?
Dragon Shout 5 Second Cooldown: Sets all dragon shout cooldowns to five seconds, because most of the vanilla cooldown times are bulls***.
Enchanting Freedom: Lets you put any armor enchantment on any piece of armor.
Saturation Boost: Makes the outdoors look less washed out.
Kagrenacs Instant Fortress: It's a house that you can place literally anywhere you want in the Tamriel worldspace, or just carry around in your inventory. A magic ring lets you teleport in and out of it from any outdoor place in the game. Perfect for when you exit a dungeon overencumbered by insane loot. Honestly, this is the only house mod I use these days.