It seems rather unfair to include any minis with this list, since that would seem to open up some other pretty crazy obscurities. The rule of thumb is likely the bigger it was, the more likely all units have been scrapped. PDP-8 seems a good choice out of this class however.
I was about to suggest the Alto, but I see it rounding out the list there. Out of the whole list, that is the one computer I would definitely like to own.
Overall, my extremely limited (no hands-on knowledge, all just lots of online reading) suggests this is an excellent list.
I will suggest Evans & Sutherland 3D graphics workstations, however. I'm told (by NeoGeoMan IIRC) that there were actually a good number of ultra high-res displays back in the day (high res even by today's standards: E&S had some 4096 x 4096 resolution monitors back in the day) in use in various places.
The E&S is always one of my first choices because it was picked by Michael Waite for inclusion in his Computer Graphics Primer, a great little resource (if limited and also not 100% correct - he does misspell Wozniak's name in one place, after all).
E&S systems were used for flight simulators and advanced molecular modeling back in the 70s-80s, and they're still around and working in the same segment. They still seem to be one of the unheralded giants of computer graphics.
There is also - the name eludes me at the moment - some early 68000 systems without monitors that were used as training devices. They have a register paper-type printer and an extended keyboard format. It sticks out in my mind because the Wikipedia article says these have been in use for years at some haunted house running certain animatronics year in and out
It's also probably not anywhere in the same class as those in your list, but the name GRiD comes to mind.