Mac OS X boot keys. Hold down as soon as possible after hearing the start-up noise and don't let go until something different happens.

key	result
shift	Safe Mode
Opt+⌘+o+f	Open Firmware
⌘+v	Verbose Mode
c	Boot from CD/DVD

The ⌘ symbol is ⌘ and ⌥ is ⌥. Actually, looking at my ⌨ (keyboard), ⌥ is now just alt.