I like the assembly suggestion, but it's a bit too much like work. At the moment I'm writing code for a Texas Instruments VLIW DSP. Most of it's in C but you have to be able to understand the assembly when the compiler screws up (as it often does). VLIW assembly code is a bit of a brain-melting experience.

On the other hand I can highly recommend microcontroller assembly as a fun way of learning about the opposite of high-level languages. PICs, with their 30-odd instructions, are the ones I've played with.

Lisp scares me, which probably makes it a good choice to learn next. I might even eventually be able to configure emacs!

--
Kevin O'Rourke