I am rather novice at modding Skyrim, so there are much better, experienced more players with detailed mods recommendation lists. However, in my single modded playthrough, I have found some mods to be purely excellent. The purpose of this page is to highlight them.
This is my favorite custom player house. It replaces Breezehome in Whiterun, and it's pretty much perfect. I have had zero bugs with this house, and also zero disappointments. While similar in size to the original Breezehome, it turns the space into a cozy, effective player home for Whiterun. It even allows for 4 children, though I found it cramped having the entire fam there, plus Lydia, plus Meeko. There are plenty of display areas for collectibles, and overall, it's an impressive house that I actively use as my base of operations.
This is more than a mere addition of flavor text. This is a complete reimagining of the Dawnguard DLC and Serana's character. It's charming story that also allows Serana to be romanced in an organic, narratively satisfying way. I can't recommend it enough. I'm in love with her, hahaha.
This is the character preset that I use for Serana. She's just gorgeous. Note: She is wearing this armor in the screenshot, separate from the mod above.
Here are my favorite armor and clothing sets: