SiN and SiN: Wages of Sin/Additional Resources
From SDA Knowledge Base
Extensive FAQ/Walkthrough by LM - a seemingly exhaustive source for all the alternate exits/entrances, secrets and such.
Quake 3 movement guides by injx - the same ideas apply to wall strafing, circle jumping, and even trilling in this game. As of 22.4.2016 the pages with the theory are missing but should be restored later.
Quake II console commands - most of these function in SiN, but read the "console" section in the "tricks and glitches" page for more details.