A rack-mounted compact would be neat to see, and an SE would be a good one to rack up because it has a fan.

Connectix RAM Doubler was software available in the '90s that did some combination of compression, virtual memory, and one or two other tricks in order to maximize the amount of RAM you had available to use. It would be neat to look at, but given that you can probably inexpensively max the memory on most of these machines using parts you may already have on hand, it may not be something you want to bother with.