Is there a checklist for securing MacOSX machines?
DISA STIGs are always good:
DISA is the Defense Information Systems Agency, the IT shop for the US Department of Defense. STIGs are the configuration guides that they publish for security networking and computing devices.
Apple has official Security configuration guides here, and there is a checklist in the appendix.
Protect the device from Firewire / DMI based attacks: Use epoxy on the physical ports, or update the OpenFirmware settings
The NSI's (slightly modified from Apple's guide) reference is here
Add a password to your OpenFirmware-based Mac