(You can also purchase a hard copy of the manual.)
To me, NASA is one of the most recognizable brands, period. Their consistent and powerful use of graphics is a big part of that fame. Consistency and power comes in large part from developing and following a style guide.
The NASA guide covers it all, too: logos, typography, page design, signage, even vehicles, uniforms and patches. They smartly saw that their brand would be very prominent in public spaces, and planned for that. Ever wondered how to brand a Gulfstream jet, the Hubble Space Telescope or the Space Shuttle? It’s in the manual.
The typography and page design sections of the manual are especially strong and informative. If you ever need guidance on these topics for yourself or for you colleagues, this is a great reference.
And of course, those fabulous NASA patches. I recently tried to talk my boss into making a version of our company logo that resembled a NASA patch. No luck so far, but I’m not giving up on the idea. Maybe some of that NASA brand strength will rub off on us.