Dwarf Fortress, a complex rogue-like game that's been in a state of constant improvement and refinement since 2002, is a masterclass in procedural generation (PCG). If you're a coder with even the slightest interest in algorithmic content creation, Procedural Generation in Game Design, a 336-page book co-edited by Dwarf Fortress developer Tarn Adams, is a must-have.
Available from Wordery for $80.59 (and various other online stores), Procedural Generation in Game Design is a joint effort by Adams and veteran designer Tanya X. Short to provide a definitive resource on the topic.
What makes the book particularly great is that it doesn't just cover the crunch of making procedural content, such as algorithms and formulas — it also points out where PCG is a bad idea and why relying on it entirely is usually a mistake.
It includes work from a variety of designers and experts, including Emily Short, Darren Grey, Dr Mark R. Johnson and Kate Compton, to name just a few.
If you're curious, you can preview the book over at CRC Press. I'd suggest reading the preface by Derek Yu (of Spelunky fame).