For their 100th QuickTips email newsletter, Seattle area mac support agency CreativeTechs has published a handy little troubleshooting guide that fits neatly in your shirt pocket. The "My Mac Won't Start!" pocketmod tiny guide is available as a free PDF download, and covers basic troubleshooting steps such as starting up in safe mode, single user mode, booting from an external device, and attempting to view the machine using target disk mode.
The QuickTips newsletter is something I've been subscribed to for a few months now, and it never fails to bring new insight into the way I use my Mac. Although aimed at creative professionals, the mailer has tips that are applicable to almost everybody, no matter their profession.