Websites
Guess the game. Guess the game presents you with 6 screenshots of a game, and from that you must guess which one it is. New one released everyday. Archipelago Multiworld randomizer. Multiworld randomizer is a way of playing different games in a co-op fashion by randomly suffling the items between the games. This site allows to easily get into this way of playing games, which is a good accesible way to share your gameplay experience with other people.
Polycosmos. Polycosmos is a mod for the game Hades so it can be used for archipelago multiworld randomizer. I am developing it, so of course I would give it a spotlight!
Godot. Godot is a free open-source game engine. If you want to start with game development, it is my best recomendation.
Itch. This is a site for game developers to freely upload and sell their game and assets. Really good alternative to steam.
Pirate Software. Even though the name is confusing, Pirate Software is an indie developer which has really useful information for game development. Also he rescue ferrets, and they are the cutest.
Tomyatemo. Tomimi is another really cool game dev. He made the Runemaster Diary, which is a really nice RPG you should check out, among other things. You can check those, some jokes and a blog on this site.
Assets
Kenney. Kenney is an awesome indie developer that produce assets and upload them. You can get a big bunch for free, or a really affordable price. Open game art. A website that contain tons of free license assets, ranging from music to sprite sheets.
Free sound. A website full of sound effects with free license to use.
Game UI database. A website having UI of every game I can possible imagine. Incredible for comparison and UI desinging.
Videos
Jason Weimann channel. Really usefull por programming tricks and tips.
GDC channel. GDC is home of the biggest game developer conference in the world, the youtube channel shares some of their bests talks.
Adam Younis channel. Adam does amazing videos on video game pixel art while working in Unity.
t3ssel8r channel. Some nice videos to procedurally generate animations.
aarthificial channel. Some good information on how programming tools can improve art and overall presentation.
Acerola channel. Really good videos about rendering and shaders.
GMTK channel. Really good analysis about game design.
Sakurai channel. Really good general game development information from the creator of the smash bros series and Kirby.
Ask Gamedev channel. Really good producing, marketting and general game dev tips from a big group of game devs.