At the moment, my gaming is limited to Diablo3 and I often find myself going to the same two sites to get inspiration for new builds and tactics: Maxroll.gg and icy-veins.com.
YouTube has heaps of channels, my favourite ones being Wudijo, Raxxanterax, and Filthy Casual.
I agree, I use Maxroll when looking at tactics or builds. I used to use Wowhead a lot as well. I watch Macrobioboi on Youtube as he talks a lot about Necromancers which is the class I currently main.
Other Youtubers I like / watch are Splattercat gaming and Lazy Peon.