Cheat sheet for directories from "Filesystem Hierarchy Standard"

The standard works for many Linux operation system distributions (though not as really strict standard).
The standard itself: http://www.pathname.com/fhs/.
This list is not precise, exhaustive - only basic outline.

• Variable:
  • /tmp
  • var
  • ~/.
• Static:
  • Architecture-specific:
    • lib
    • bin
    • sbin
  • Non-architecture-specific:
    • etc
    • share

"Hierarchies":

• /
• /usr
• /usr/local
• /opt

Directories usual to lie in "hierarchies":

• etc
• share
• lib
• bin
• sbin

"/var" subdirectories:

• cache
• lib
• spool
• run
• log

Directories of "/" and not other "hierarchies":

• tmp
• home
• root
• mnt
• media
• boot
• srv

Package-specific:

• ~/.
• /opt/ (/opt/provider)

That's all.
Yes, and at the end, some interesting directories from "Debian Policy Manual" (http://www.debian.org/doc/debian-policy/):

• /etc/skel
• /var/log/.log
• /usr/share/{man|doc|info}