Building keyboards
Saintcon 2016 HHV Presentation Stuff
Slides
Keyboard Forums & Resources
Mechanical keyboards subreddit
Geekhack: the oldest(?) and biggest keyboard forum
Deskthority: Keeper of the Great Wiki
Massdrop: Only for buying stuff. Hosts many group buys.
Keyboard Firmware
TMK Firmware, most common
QMK Firmware, originally TMK fork, now much more. My curent FW of choice.
Kiibohd: up and coming firmware for faster ARM micros
Firmware Tutorials
matt3o: How to build your own keyboard firmware (TMK)
Kiibohd usage tutorial for Teensy 3.x