1. mouse down >> Eject removable media
2. opt >> Bring up OF system picker on New World machines
3. cmd-opt >> Hold down until 2nd chime, will boot into Mac OS 9 ?
4. cmd-x (or just x?) >> Will boot into Mac OS X if 9 and X are on the same partition and that’s the partition you’re booting from.
5. cmd-opt-shift-delete >> Bypass startup drive and boot from external (or CD). This actually forces the system to NOT load the driver for the default volume,
6. cmd-opt-shift-delete-# >> Boot from a specific SCSI ID # (# = SCSI ID number)
7. cmd-opt-p-r >> Zap PRAM. Hold down until second chime.
8. cmd-opt-n-v >> Clear NV RAM. Similar to reset-all in Open Firmware.
9. cmd-opt-o-f  >> Boot into open firmware
10. cmd-opt-t-v >> Force Quadra AV machines to use TV as a monitor
11. cmd-opt-x-o >> Boot from ROM (Mac Classic only)
12. cmd-opt-a-v >> Force an AV monitor to be recognized as one
13. c >> Boot from CD. If set to boot to X and no CD is present, may boot to 9.
14. d >> Force the internal hard disk to be the startup device
15. n >> Hold down until Mac logo, will attempt to boot from network server (using BOOTP or TFTP)
16. r >> Force PowerBooks to reset the screen
17. t >> Put FireWire machine into FireWire Target Disk mode
18. z >> Attempt to boot using the devalias zip from first bootable partition found
19. shift >> (Classic only) Disable Extensions
20. shift >> (OS X, 10.1.3 and later) Disables login items. Also disables non-essential kernel extensions (safe boot mode)
21. cmd >> (Classic only) Boot with Virtual Memory off
22. space >> (Classic only) Trigger extension manager at boot-up
23. cmd-v >> (OS X only) show console messages during boot
24. cmd-s >> (OS X only) boot into single user mode