Developer Resource List
Please see below a list of links to game development resources. There's quite a variety here, so whatever you're looking for you should be able to find what you need.
If you know of any other resources or wish to be featured in this list, please email me on email@example.com.
Hailing from the Netherlands, Kenney.nl is a fantastic resource and whilst a lot of developers know his work for the amazing sprites he produces, there is a whole host of game development goodies here. The include; games he makes himself, 3d models music, sound effects & software. There really is something for everyone and nearly any sort of game you want to produce.
Best of all, nearly the entirety of it is free and all assets are licenced under the CC0 1.0 Universal licence, meaning you can use it personally, or commercially.
Like I said, most of it is free but the stuff that does cost money is definitely worth paying for, there's Asset Forge (which comes in "Standard" & "Deluxe" forms), which makes it really easy to put together 3D models from component pieces of varying themes. This is great if you're not much of a modeller yourself (like me).
In the paid packages there's also 2D & 3D game assets that you won't find elsewhere, you can find these in Kenney's itch.io page.
Graphical Effects (GFX)
Sound Effects (SFX)
Unity Unreal Engine 4 Godot