In one of the boxes from the attic, I found a couple of really neat Topps Micro Sets from 92 and 93. From what I can tell, these two years, as well as 91 were the only years Topps put this product out. I wish they would issue them again, because they are really cool. Here are some of the cards next to a standard mini card and a penny for scale:
I felt very old looking at these cards, alternately holding them closer and further and closer again to my eyes trying to find the right distance to gain focus. I didn't include it in the scan, but there are checklists in this set. I defy anyone without a microscope to read them. The 1992 set also included a 12 card "Gold" bonus set.
They also were one step ahead of themselves on the Diamond Parallel cards everybody is snapping up this year. The 1993 factory set came with a set of 12 "Prism" Cards: