Procedural Content Generation in Games is an in-development-textbook about games and procedural content by Noor Shaker, Julian Togelius, and Mark J. Nelson, plus a ton of contributing writers. 

As mentioned by renderfck in reply to the question about tutorials, it’s a good next step for learning about more advanced procedural generation. It’s got detailed technical breakdowns of various techniques, with a focus on approaches that are useful in playable, interactive situations. I want to cover the chapters here individually at some point, but if you’re interested in any of the content of this blog, you’ll probably want to read the book long before I get around to doing that.