UE4 Useful Links

Official Sites
Getting Started Docs
Unreal Online Learning
Reduce Your Package Size 
Tutorials and Guides
Blueprint Getting Started Thread
C++ Getting Started Thread
Community Wiki

Unreal Engine’s Official YouTube Channel
DevSquad’s Youtube Channel
Lusiogenic’s Youtube Channel
DevAddict’s Youtube Channel
Mathew Wadstein’s YouTube Channel
Peter L Newton’s YouTube Channel
TeslaDev’s YouTube Channel
Luos’ YouTube Channel
GameDevMan’s Youtube Channel

Tutorials and Guides
Tutorials by Tom Looman
Blueprint Guides by Romero