...from the experts:
Training, Courses, Classes

Hilf GmbH offer open classes and inhouse training for MC68HC12/MC9S12X and many other microcontroller architectures

...go for a deep dive:
Project Articles on hc12web.de
The ACPRD Project Page
The RAM.Bo256 Project Page
The DIS12 Project Page
Project RAM.Bo32
RAM! Mehr RAM!
HC12 Review
Schnellstart mit dem HC12

...things to explore:
Directory of HC12 Links and Resources
Overview HC12 Derivatives
Links to HC12 Resources on Freescale Servers
Mailing Lists and Newsgroups
Shareware and Free Software incl. Code Samples for the HC12
HC12 Community: Projects, Links, Resources
Articles published in Magazines or Online
Books on the HC12
Training, Courses, Classes
Commercial HC12 Development Tools: Compilers, Debuggers, Emulators
HC12 Evaluation Boards, Controller Modules and Single Board Computers
Fuzzy using HC12 Microcontrollers