dryad.technology/artist/
Become a great artist in 10 seconds with this cool glitch-texture-thing!
Texture Ninja
Huge repository of public domain textures available to download without any bullshit
Symbol Sanatorium
Huge Google doc with a ton of symbols, kaomojis & text layouts!
Smithsonian Open Access
Over 5 million images from the Smithsonian's collection, totally free to download & use!
Universal Hint System
Useful if you're stuck in a game and don't want to resort to using a walkthrough.
In the same vein...
Before I Play
Things that'd be nice to know before you actually get to playing, like if there's a time limit (I hate those!)