Hi,
You could look at the ColdFire line of processors as they are a direct descendant of the 68000.
I'd recommend you take a look at the ARM processor too as it seems to be the post popular processor these days, and programming it in assembly language has some very practical uses. If you have a linux box/vm you can get started programming it with this tutorial and QEMU
http://bravegnu.org/gnu-eprog/index.html
