(I will constantly edit this post to add what I know. Please add your own suggestions in the comments)
Books: (links go to Amazon)
-Computational beauty of nature by Gary William Flake.
Great book, goes over lots of ideas about how you can write code imitations of the wonderful patterns of nature. He includes source code to his books written in C, I have often looked at these while coding myself.
-The Fractal Geometry Of Nature by Benoit B. Mandelbrot
Mandelbrot coined the word "fractal", brought the field into the computer age and discovered the Mandelbrot set.
-Real Time Rendering (parts, some include) 11.1 Sources of three-dimensional data pg 438
-Texturing & Modeling: A Procedural Approach
-Computer Graphics by Foley, Van Damme etc - various chapters
-Graphics gems - Various techniques spread out among the (many) books
The AI System for Left 4 Dead by Valve -article describing procedural gameplay. Left 4 Dead is a first person shooter where you are part of a small team and have to fight your way out through a zombie hoarde. The monsters, guns and excitement level is adjusted based on the intensity of the player experience.
The demoscene uses procedural graphics to generate impressive scenes in incredibly small code sizes. A collection of some on pouet.net