Almost all of them are for ACNL & ACWW because they're the ones I play the most, sorry!
Mirrored on my Animal Crossing page/shrine

General + Misc

chriiscrossing	Masterpost of the little villager pixels
My ACWW diary	ACWW | How to lock villagers into staying forever. This blogs has other usful tips too!
Mori db	ACNL | Item database
Mischacrossing	ACNL | General tips for landscaping
El Taller de Al	ACNL | In spanish, pics of every item variant/customization
AC Camp	A pretty funny liveblog of ACWW

Patterns

Vivicore	Brick pattern tutorial
A forest life	ACWW | General paths. Please check the rest of site too!
LaFra's QR pack	ACNL | What the tin says, a mega pack with +500 QRs. If you saw a popular path in 2014, it's probably here!
Hiyokodesign	ACNL | Clothing and some paths & cutouts
Ririalice	ACNL | My favorite pattern maker! Pink fairytale paths and clothes
Alicemignon12	ACNL | Pastel dessert & fairytale
Rokumeikanmura	ACNL | Natural & food
Besaid Designs	ACNL & ACNH | Natual & fancy. ACNL is mostly fake grass patterns.
Bibi design	ACNL & ACNH | Bricks, flowers... Has lots of clothes too
Soeurs doigts de fee	ACNL | French site with a bunch of QRs

Hacking

ACNL editor	ACNL | Town save editor. Freely change your town, villager, houses, character's names...
Custom flags	ACNL | To be used with the save editor, flags for customized furniture
ACNL REditor	ACNL | Havent used it yet, but seems a much more complete save editor
Briclyn Forest	ACNL | How to get trails of anything when walking