Keep one of these keys pressed at system start:
| ⌘ | Command key |
| ⌃ | Control key |
| ⌥ | Option key |
| ⇧ | Shift Key |
| ⇪ | Caps Lock |
| fn | Function Key |
| C | Boots from a CD/DVD with a system image |
| D | Boots from the first HD partition |
| N | Boots from the network (netboot) |
| R | Enforces a screen reset |
| T | Boots in firewire target mode |
| ⇧ | Boots in safe mode. Disables login items and less important kernel files |
| ⌘V | Boots in verbose mode |
| ⌘S | Boots in single-user mode. Goes directly into command-line |
| ⌥ | Displays possible startup disks |
| ⌘R | Boots in recovery mode. Allows to reinstall the Operating System |
… and much more: http://support.apple.com/kb/HT1343