Apple Boot Key Combos:

Bypass startup drive and boot from external (or CD) 
CMD-OPT-SHIFT-DELETE
Boot from CD (Most late model Apples)
C
Boot from a specific SCSI ID #.(#=SCSI ID number) 
CMD-OPT-SHIFT-DELETE-#
Zap PRAM 
CMD-OPT-P-R
Disable Extensions 
SHIFT
Rebuild Desktop 
CMD-OPT
Close finder windows.(hold just before finder starts) 
OPT
Boot with Virtual Memory off 
CMD
Trigger extension manager at boot-up
SPACE
Force Quadra av machines to use TV as a monitor 
CMD-OPT-T-V
Boot from ROM (Mac Classic only) 
CMD-OPT-X-O
Force PowerBooks to reset the screen
R
Force an AV monitor to be recognized as one
CMD-OPT-A-V
Eject Boot Floppy 
Hold Down Mouse Button
Select volume to start from 
OPT
Start in Firewire drive mode 
T
Startup in OSX if OS9 and OXS in boot partition 
X or CMD-X
Hold down until the 2nd chime, will boot into 9? 
CMD-OPT
OSX: Watch the status of the system load 
CMD-V
OSX: Enter single-user mode (shell-level mode) 
CMD-S
 

After startup:

Bring up dialogue for shutdown/sleep/restart
POWER
Eject a Floppy Disk
CMD-SHIFT-1 or(2) or (0)
Force current app to quit
CMD-OPT-ESC
Unconditionally reboot
CTRL-CMD-POWER
Fast Shutdown
CTRL-CMD-OPT-POWER
Goto the debugger (if MacsBug is installed)
CMD-POWER
Put late model PowerBooks & Desktops to sleep
CMD-OPT-POWER
 

Application Specific Keys:

Startup key combos to reset the resolution on video boards:
SuperMac (at least some models)press&hold
OPT
Imagine 128 Card (reset resolution)
N
RasterOps (at least some models)press&hold
CMD-OPT-SHIFT
Radius (Use cable sense pins to set resolution)
U
Radius (Cycle through available resolutions)
T
 
Conflict Catcher:
Pause Boot
P
Launch CC at Startup
SPACE or CAPS LOCK
Skip remaining extensions
CMD-PERIOD
Reboot cleanly while loading extensions
CMD-R
 
RAM Doubler:
Disable at Startup
~ (Tilde) or ESC
 
Apple System Installer:
Change custom install to clean install
CMD-Shift-K
 
Claris Emailer:
Bypass specified startup connections
Hold CMD at launch
Bring up rebuild options
Hold OPT at launch

 

 

Boot ROM

 

 

Command-Option-P-R

Zap PRAM (double boot)

R

Force PowerBook to reset the screen

Command-Option-A-V

Force an AV monitor to be recognized as one

Command-Option-T-V

Force Quadra AV to use TV as a monitor

Command-Option-X-O

Boot from ROM (Mac Classic only)

Mouse button

Eject Floppy, then boot from SCSI

Command-Option-Shift-Delete

Bypass startup drive (boot from the first bootable device other than the normal boot device).

Command-Option-Shift-Delete-#

Boot from a specific SCSI ID, where # is 0 through 6

C

Boot from internal CD-ROM (Most late model Macs)

N

Boot from network (iMac and later models)

D

Boot from the internal disk if the default boot device has been set to something else

Z

Boot from an internal Zip drive

O-F

Access Open Firmware (on G3 and later models)

T

Boot into FireWire Target Disk mode (on certain FireWire-equipped PowerBook)

Upon appearance of the happy face, let go of any boot keys you may have needed, then immediately press any keys you need to control ...

Mac OS System startup

 

 

Command

Boot with Virtual Memory off

Shift

Disable all Extensions and Control Panels. Release Shift when the message "Extensions disabled" appears in the welcome box.

Space

Open extension manager before loading Extensions or Control Panels. Release the Space bar when the Extensions Manager displays its screen.

Holding the Shift key early in the boot sequence disables all Extensions and Control Panels. Individual Extensions and Control Panels may disable themselves upon seeing the Shift key later in the boot sequence, but the timing for this is difficult to achieve! Upon loading, an Extension or Control Panel is supposed to display its icon in the "icon parade." If the icon is displayed at boot time, but the Extension or Control Panel disables because the Shift key is held or some error condition is detected, it is conventional for a red X to be drawn over its icon.

Immediately upon the appearance of the (blank) menu bar, press any keys you need to control ...

Finder startup

 

 

Command-Option

Rebuild Desktop

Option

Start without opening finder windows

After startup

Lots of Finder shortcuts are documented in the online Finder Help. (p.s. Don't delete that file: Certain Apple installers refuse to function unless that file is in its proper place.)

 

 

Command-Shift-1 (or 2, or 0)

Eject a Floppy Disk [FKEYs]

Command-Option-ESC

Force current app to quit.

Command-POWER

Invoke the debugger (if MacsBug is installed) - G to return to interrupted code

Restart, Sleep, Shutdown

If you have a Power key, it is at the top of your keyboard, at the center or on the right hand side; it carries an incused triangle symbol.

 

 

POWER

Present Restart, Sleep, Shutdown dialog - key R for Restart, S for Sleep, ESC for cancel, or Return for Shutdown.

Control-Command-Option-POWER

Fast Shutdown

Command-Option-POWER

Put late model PowerBooks & Desktops to sleep

Control-Command-POWER

Unconditional, forced reboot (the "three-finger salute")