Good Vintage Computers?

The Crooked Elf asks: "I'm going to be running an event dedicated to vintage computers and game consoles in a month for the computer science department at the University of Southern Maine. My current arsenal includes a TRS-80 Color Computer 3 and an old NES (with Zelda, Mario, etc), but I feel I need a few more items to display. I have a budget of around $600 for this event. Slashdot, what do you feel are other decent vintage systems that would be the most valuable and educational to present?"