For my own sake, and of course anyone else who will find these useful, below are a list of resources that I use for WoW Classic. They are in alphabetical order.

General

CurseForge Addons – Find any addon you need for WoW.
Wowhead – A great resource for all things WoW Classic: items, questing, news, etc.
Wowhead Talent Calculator – Help you figure out your talents before you commit to it in game.

Hunter

Pet Name Generator – A pet name generator I created for Hunters.
Petopia – The most useful Hunter resource you’ll find regarding pets.
Petopia for TBC – With TBC being all but confirmed at this point, here’s an archive of Petopia for TBC.
Wowhead Pet Training Calculator – A great tool for figuring out your pet training