First of all. What is procedural content generation? There is a wiki for that.
“Procedural content generation (PCG) is the programmatic generation of game content using a random or pseudo-random process that results in an unpredictable range of possible game play spaces”
These are some of my bookmarks concerning all things procedural:
Develop Magazine, on No Mans Sky. Just click it.
“Develop speaks to seasoned developers on why they are embracing automatic creation” Here.
The heavy stuff:
Guides & tutorials:
Tips for using procedural content in games.
Procedural audio in unity. Link.
Procedural color generation.
Hex system guide.
Procedural geometry in unity: Link
PCG in games :Rescue on Fractalus (1985); Dwarf Fortress (2002);