I'll post some tutorial type stuff for mappers and modelers:
  1. Good to check this one like once a week for updates.
  2. Valve's official developer wiki, always good.
  3. Awesome place for weapon references (used by the developers of STALKER too )
  4. Exporting from 3DS Max
  5. IF YOU ARE A NEW MAPPER LOOK AT THESE NOW.
  6. Useful for texturers
  7. Animating a weapon for CSS
  8. Great texturing tutorial for hard surfaces
  9. Tutorial for people who don't know how to bake AO maps (required for the tutorial above)
  10. Great place to get custom brushes