And this is why AmigaOS is so great, even 30 years later. 
Agreed! Actually 1 of many reasons.
You didn't mention which Amiga or version of the OS you have. If you still have the books that came with an OS1.3 Amiga, the small book "Enhancer Software" has a complete list of all the traditional directories and all the files they contain on the standard disks (starting at B-1). As already said, most of the AmigaDos manuals explain this well, too.
One of my favorite references is Rob Peck's "The Amiga Companion". It is clearly written and available online as a PDF.
@ Chris
"..L - Filesystem Handlers (named Libraries due to TripOS legacy).." I used to wonder about how L got its name.
