For Mac OS X fans-a few will become my friends

keys to hold down=
C = starts up from a CD
D = starts up from the first partion
N = starts up from network server
R = resets the powerbook screen
T = puts the Mac into firewire target disk mode
X = starts up in Mac OS X (if 9 is on the same disk)
Option = shows icons of all startup diskd, so you can choose one for starting up
Shift+option+apple+delete = starts up from external drive (or CD)
Option+apple+P+R = zaps the parameter RAM (PRAM). (hold down until second chime)
Option+apple+O+F = brings up open firmware screen
Apple+V = shows unix console messages during startup, logout, and shutdown.
Apple+S = starts up in single user (Unix command-line) mode
Mouse down = ejects a stuck CD or DVD
Shift = just after powering up: Turns off kernel extensions
Shift = Later: After logging in: Prevents Finder windows and startup items from opening. (They'll return the next time you start up.)

In the Finder
Option+apple+W = Closes all Finder windows
Right arrow, Left arrow = Expands or collapses a selected folder in list view
Option+right arrow = Expands a folder in a list view and all folders inside it
Option+left arrow = Collapses folder and all folders inside
Apple+up arrow = Opens parent folder
Shift+Option+Apple+up arrow = Selects the desktop
Apple+down arrow = Opens the selected item
Option+click the flippy triangle = Expands or colapses all folders within that window
Tab = Selects next icon alphabetically
Shift+Tab = Selects previous icon alphabetically
Apple+Delete = Moves highlighted icons to the Trash
Space bar = Opens the disk or folder under mouse immediately (during a spring-loaded folder drag)
Shift+Applw+Q = Logs out
Shift+Option+Apple+Q = Logs out without confirmation box
Shift+Apple+Delete = Empties the Trash
Shift+Option+Apple+Delete = Empties the Trash without confirmation box
Option+"Empty Trash" = Empties the Trash without confirmation box
Option+Apple+drag = Scrolls a Finder window in any direction (icon view)
Option+click the Zoom button = Enlarges the window to full screen
Option+click Close button = Closes all Finder windows
Apple+drag an icon = Moves it into, or out of, the system folder (administrator password required)