Some useful startup keys for Mac:
- C : Force boot from the CD-Rom drive
- D : Force boot from the internal hard drive
- Option : System picker show all bootable disks
- Space Bar : Apple extension manager
- Command-S : Boots Mac OS X into “Single User” mode
- Command-V : Boots Mac OS X into “Verbose Mode”
- Command-Option-P-R : Erases PRAM if held down immediately after startup tone
- Command-Option-N-V : Erases NVRAM
More at MacOSX Things and OtherWorldComputing