Please note that a lot of these modules are very rare! (And also I am now counting Rackmount Modules)
While I myself are looking for and listing them as I find them (I should make a post with the ones I do find and edit it as I go.), I am only one person, I can't really do this by myself very well. (please do not try to read this sentence too much)
You know what, this post is the one that gets the list, I don't want to make a separate post just for the stupid list. This will be marked as the solution so it's easy to find.
GZ-50M GM sound module, rather small.
GZ-70S GM MIDI speakers, Japan exclusive
GZ-30M smaller GZ-50M and also Japan exclusive.
WP-150 PCMCIA midi module, similar to the GZ-50M
VZ-10M Uses Casio's wonderful iPD sound source. It's a VZ-1 but as a MIDI module. You can link multiple of these together to create a larger, more complex synth.
CSM-1 Casio Sound Module. It was an older one that came out in the 80s. Also, Japan Exclusive AFAIK.
CSM-10P a CSM-1, but only for certain instruments, might have been designed to be paired with the CSM-1. It's a piano module.
VZ-8M Essentially half a VZ-10M in multiple ways. Could connect to the VZ-10M and VZ-1 synths to give them more functionality.
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