I always seem to forget these so I'm putting them here so I know where to find them next time I forget :)
Command-S Boot into Single User Mode
Command-V Boot using "Verbose" mode (shows all kernel and startup console messages)
X Reset startup disk selection and boot into Mac OS X Server
Shift Boot into "Safe Boot" mode, which runs Disk First Aid. A reboot will be required afterward.
Option Boot into Open Firmware to select a boot device
Command-Option-Shift-Delete Bypass internal harddrive on boot
T Boot into Firewire target disk mode
C Boot from the internal optical drive
N Start from the Network (NetBoot)
Command-Option-P-R Reset Parameter RAM (PRAM) and non-volatile RAM (NVRAM)
(mouse button) Eject (internal) removable media
ALSO: if you use open firmware password... you'll need this:
Startup Manager -accessed by pressing the Option key during startup
Enter commands after starting up in Open Firmware -press Command-Option-O-F key combination during startup.
How to troubleshoot a computer with Open Firmware Password enabled
If you cannot access the Open Firmware Password application and need to troubleshoot your computer by:
Resetting the PRAM
Starting up in Single-user mode
Starting up in Verbose mode
Starting from CD-ROM
Then follow these steps:
Start up into Open Firmware by pressing and holding the Command-Option-O-F key combination during startup.
At the Open Firmware prompt, type: reset-nvram
When prompted for your password, enter it and press the Return key. It responds OK.
At the Open Firmware prompt, type: reset-all
The computer restarts and you are now be able to reset the PRAM and startup in Single-user mode, Verbose mode, or from CD-ROM. Reference Link