FINDER KEYBOARD SHORTCUTS They must be used from the Finder, not from an application.
cmd+N - Create a new folder
cmd+Down Arrow - Open a File or Folder
cmd+O (letter) or cmd+Down Arrow - Open a highlighted icon
Tab - Select the next alphabetical icon
shft+Tab - Select the previous alphabetical icon
Left Arrow (in icon view only)Select an icon to the left
Right Arrow (In icon view only) - Select an icon to the right
Up Arrow - Select an icon (or file) above
Down Arrow - Select an icon (or file) below
cmd+D - Duplicate a selected item
opt+Up Arrow - Open parent window
cmd+W - Close the Active Window
opt+click on folder triangle (list view) - Expand Folder and all contained within it
opt+click on folder triangle (list view) - Collapse Folder and all contained within it
cmd+opt+W - Close all open windows -(or opt+Close from the File menu or opt+clicking any window's close box)
cmd+dragging window's title bar - Move Inactive Window
cmd+I - Get Info
cmd+del - Move selection to the trash
cmd+opt while inserting disk - Rebuild Floppy Disk Desktop
cmd+opt+Tab while inserting disk - Erase Floppy Disk
opt+drag - will make a copy of an item instead of just moving it

Some of the most common shortcuts that are available to virtually all Mac programs are:
cmd+A - Select All items or text in active window
cmd+C - Copy the current selection to the clipboard
cmd+O - Open a file
cmd+P - Print the active window
cmd+Q - Quit the active application
cmd+S - Save the current file or document
cmd+V - Paste clipboard contents at current cursor position
cmd+W - Close active window
cmd+X - Cut the current selection, delete it from current window and put it on the clipboard
cmd+Z - Undo the last action

Control Your Machine While Booting Up:
shft - allows you to start up your Mac without extensions.
C - allows you to force your Mac to boot from an internal CD-ROM drive.
cmd+opt - tells the Mac to rebuild the hidden Desktop file. This should be done periodically for good preventative maintenance.
cmd+opt+shft+delete - tells the Mac to skip the first device in the SCSI chain. This comes in handy when you want to force your Mac to boot from an external drive.
cmd+opt+P+R - clears the Parameter RAM. One of those things to do when things aren't right and you can't think of anything else to try. This clears things like date and time, location, etc.
Spacebar - opens the Extensions Manager when starting up.
Mouse Button - will force eject a floppy while booting up.
opt (OS9) - will allow you to choose which disk or volume to boot from