My display cabinet for quite dome time was a series of cardboard boxes stored in my roof space (I'm ashamed to say).
Recently I've hung an IKEA "Bertby" cabinet (easier to google for it than provide an enormous link).
This looks pretty nice and is small enough to sit in an out-of-the -way place, but squeezing an HP97 in there is an interesting trick. I've also found that I can slope the glass shelves a little and the door when closed will stop them sliding out (the sort of ooze forward over 24 hours or so). A little bit of rubber matting behind the calculators stops them from slipping.
I've managed to squeeze a fairly broad selection of calculators in there, but it's not ideal.