Under IBM, the M SSK should be called the "IBM Space Saving Keyboard".
There's also the M4 and its variants.
The later r/d versions with trackpoints are the "IBM Space Saver" (blue enter key and IBM logo on right as top edge is notched on left), and the "IBM Space Saver II" (all black keys with IBM logo on left).
As well as the "external thinkpad keyboard", the UltraNav (there are a few variations of those too).