Programming Languages
The MC 68HC11 is so popular because of the numerous amount of programming support available. A free C-compiler are available as open source as Gnu embedded C. Also available are Basic interpreters, Forth, TASM, editors and assembler for the Mac. There are numerous simulators and emulators available as well for
The GNU C development chain for 68HC11: Open source freeware that includes a bunch of libraries.
Basic Compiler: This is essentially what is used for the Lego Mindstorm.
68HC11 Assembler for the Mac: So the Mac guys don't feel left out.
THRsim : A 68HC11 simulator - There is a free demo but the full version is only $50.
Help File: A complete help guide to the 68HC11 instruction set.
Various emulator are also available.
A full FAQ is available at: http://www.faqs.org/faqs/microcontroller-faq/68hc11/