These shortcuts are curtosy Macworld magazine

Command-S = Single User mode (provides access to the command line).

Command-V = Verbose mode.

Option = Takes you to a screen where you can select the volume you wish to boot from.

Command-Option-P-R = Zaps the PRAM.

X = Boots from the OS X volume.

C = Boots from the CD/DVD drive.

N = NetBoot (boots from a network server).

R = Force PowerBook screen reset.

T = Boots the Mac into FireWire Target Disk Mode.

Command-Option-O-F = Boots into Open Firmware.

Command-Option-Shift-Delete = Boots the Mac from a volume other than the one designated in the Startup Disk system preference.

Shift = Safe Boot when you hold it down as you start up the Mac. Holding Shift down after the list of services begins to appear disables auto-login. Holding Shift after you've logged on disables login items.