Tex Murphy of course.
Under a Killing Moon
The Pandora Directive
Overseer
There's also
Ripper - well , sort of detective game. 6 cd-roms.
Black Dahlia - possibly the largest game ever since it consists of 8 cd-roms !
X-files : the FMV game - well , you don't actually play Mulder or Scully but a new agent who interacts within the world of the x-files. It's actually pretty cool. The PC version is 7 cd-roms while the PSX is shorten to 4 discs !