For the web developers who might want to dip a toe into procgen for the first time, I'm maintaining a mostly javascript-centric resource / links list on the subject. It includes libraries / packages, tutorials, technical / motivational videos and datasets. https://github.com/kchapelier/procedural-generation
As for assets, OpenGameArt.org is always a good website to keep on hand. For 2D tilesets I'd recommend checking the creations of Michele 'Buch' Bucelli.