Tip; Keyboard Shortcuts at Mac OS X Startup

Here's a list from Apple's own keyboard shortcut documentation and personal experience:

-X during startup - Force Mac OS X startup

-Option - (eventually) brings up a screen with startup volume choices

-Option-Command-Shift-Delete - Bypass primary startup volume and seek a different startup volume (such as a CD or external disk)

-C - Start up from a CD that has a system folder

-N - Attempt to start up from a compatible network server (NetBoot)

-T - Start up in FireWire Target Disk mode (very handy for plugging your Mac into another as an external hard drive)

-Shift - start up in Safe Boot mode and temporarily disable login items and non-essential kernel extension files (Mac OS X 10.2 and later)

-Command-V - Start up in Verbose mode.

-Command-S - Start up in Single-User mode

-cmd-opt-p-r - Zap PRAM. Hold down until second chime.

-cmd-opt-n-v - Clear NV RAM. Similar to reset-all in Open Firmware.

-cmd-opt-o-f - Boot into open firmware

-Hold mouse click - Force eject a CD/DVD