Forth! I was programming in those days myself (though only a little bit on CP/M), and was getting surprised that many people here seemed to think the only alternatives were C or assembly. I learned to program in Basic, then learned some assembly, and finally discovered Forth circa 1984. It was perfectly suited to developing on 8-bit machines -- about as powerful as C, trivial to compile, easy to drop into assembly if you needed to optimize a low-level function.

If I remember correctly, I didn't learn C until 1989, when I was working on 16-bit machines...