The top tier villager list site, this site, a German AC board and villagerdb. The essentials, I guess. Oh and I subscribed to quite a few AC players on Youtube.
I've got a few! Friendship Mechanics Guide - datamined info on how to improve friendship and where you can gain and lose points. Lost Item Guide - this is really useful when you investigate a lost item and still don't know who it is. Unfortunately I have 3 Normal's on my island so it's usually still a guessing game Personality Subtypes - So each villager has their primary personality type, but they also have a personality subtype! This is a handy chart to figure out which villagers have which subtype and how they're different from each other. I found it interesting! MeteoNook - I found my weather seed by going back to my last meteor shower in May and logging the stars by the hour and minute. Took about 20 minutes of watching for stars carefully and I found my seed! Really helpful to know, but it can be super tedious to fill in the info without a meteor shower. Nook Plaza - I like this item catalog because has info on the styles and themes of items, which helps when gifting villagers clothing and decorating my house.
I've been actually following a lot of animal crossing-related Instagrams lately. They're so many! I also regularly visit VillagerDB to look at catalog items -- I find it very easy to navigate to find ACNH only items!
Yue Crossing has a great instagram with new guides.
8bit is also another instagram that I follow!