Castellan, I use the
Imagecraft HC11 compiler and IDE. It is pretty good, although it runs under Windows. It's more or less the only reason I use Windows these days.
There is a demo version on their website, I think it lasts for a month before timing out.
I spend a lot of time writing embedded software for the HC11, mainly in C. The few times I have to resort to assembler (like ISRs), I usually write it in C first, then modify the compiler's assembler output for speed.
tony