Exhibits for a Museum of Computing
Scott Aaronson addresses this particular question on his blog Shtetl-Optimized when considering the timeline of Computer Science. The relevant posts in chronological order:

Timeline of Computer Science

Top 150 computer science events to be decided once and for all

CS timeline voting: the results are in!

Most of the events in his list would make good exhibits, although it might be difficult to figure out how to present some of them physically.