kernel.org
mailing lists on kernel.org (main communication platform for kernel devs)
lowlevel.eu (german)
kernelnewbies.org (not that great, but didn’t want to leave it out)
Jonas Berlin VGA initialization
Chris Giese VGA initialization
C++ Reference (best I know – I use it all the time)
gnu.org tutorial on inline assembler
Graphics File Format Specifications (archived)
A list of very informative – or at least interesting – YouTube Videos
A list of puzzle-games on steam, that I find interesting for nerds.
Also a list of surreal games on steam, that may be off topic here, but anyways.