Here's my seconding for both Buckaroo Banzai (love that movie) and Ringworld.
Ringworld was an amazing RPG just for the background material of Known Space - heck, when Niven recruited people to write the Man-Kzin Wars novels, instead of giving them a tutorial on Known Space, he just sent them a photocopy of the RPG.
I want that back in print, I don't care WHAT system it is for.