This is my short list with the best of the settlement mods available in my personal opinion. There are a LOT of really great settlement mods out there and I've got a guide that lists most of them if you're looking for hidden gems or have different taste (or building needs) than I do.  I personally trend towards clean or at least shabby chic but for this list I'll include postwar for you destroyed look lovers out there.

See the full guide for authors and more information on the following mods.

Automation/Utility  

Color Series

(same objects in multiple colors/prints):

Decor & Furniture

Everything & Kitchen Sink

Functionally Important

Gambling

Gorgeous Beyond Compare

Power

Saving/Transferring Your Builds

Structural

Textures

Theme: Classic Fallout

Theme: Faction

Theme: Institute

Theme: Vault


I'm totally biased on these (mods by the Creative team)