Start up from a bootable CD or DVD, such as the Mac OS X Install disc that came with the computer
Press C during startup.

Start up in Apple Hardware Test (AHT), if the Install DVD 1 is in the computer
Press D during startup.

Reset NVRAM
Press Option-Command-P-R until you hear two beeps.

Starts into Startup Manager, where you can select a Mac OS X volume to start from. Note: Press N to make the first bootable Network volume appear as well
Press Option during startup.

Ejects any removable media, such as an optical disc
Press Eject, F12, or hold the mouse (/trackpad) button.

Attempt to start up from a compatible network server (NetBoot)
Press N during startup.

Start up in FireWire Target Disk mode
Press T during startup.

Start up in Safe Boot mode and temporarily disable login items
Press Shift during startup.

Start up in Verbose mode
Press Command-V during startup.

Start up in Single-User mode
Press Command-S during startup.

Start from a NetBoot server using the default boot image
Press Option-N during startup.