I've had a great experience with two paid resources: CGCookie.com and blendermarket.com. CGCookie is a monthly subscription site that has courses on modeling, materials, sculpting, and a lot more. They just refreshed their course on mesh modeling for Blender 2.8x [1].
Blender Market can be hit or miss since it is user-created content that varies from really amateur to quite professional. If you want to learn the ins and outs of shaders in Blender, I highly recommend these two courses from the user "Blender Insight" [2][3]