Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.
I've tested all of these out. Some do not work on my keyboard, but your mileage may vary….
Key
Windows 8 Functionality
Windows logo key+spacebar
Switch input language and keyboard layout
Windows logo key+O
Locks device orientation
Windows logo key+Y
Temporarily peeks at the desktop
Windows logo key+V
Cycles through toasts
Windows logo key+Shift+V
Cycles through toasts in reverse order
Windows logo key+Enter
Launches Narrator
Windows logo key+PgUp
Moves Metro to the monitor on the left
Windows logo key+PgDown
Moves Metro to the monitor on the right
Windows logo key+Shift+.
Moves the gutter to the left (snaps an application)
Windows logo key+.
Moves the gutter to the right (snaps an application)
Windows logo key+C
Opens Charms menu
Windows logo key+Shift+C
Open Charms bar
Windows logo key+I
Opens Settings charm
Windows logo key+K
Opens Connect charm
Windows logo key+H
Opens Share charm
Windows logo key+Q
Opens Search pane
Windows logo key+W
Opens Settings Search app
Windows logo key+F
Opens File Search app
Windows logo key+Tab
Cycles through Metro apps
Windows logo key+Shift+Tab
Cycles through Metro apps in reverse order
Windows logo key+Ctrl+Tab
Cycles through Metro apps and snaps them as they are cycled
Windows logo key+Z
Opens App Bar
Windows logo key+/
Initiates IME reconversion
Windows logo key+J
Swaps foreground between the snapped and filled apps