My favorite ones would show you a grid representing all the clusters on the disk. You would see an open block for free space and a solid block for allocated space.
Then it would highlight a span of blocks to indicate reading.
Finally it would write those clusters elsewhere, indicating so with a different color.
Neat. I had one for DOS too that would go left-to-right instead of top-to-bottom, but I don't remember if it was a Norton tool or something else. It was mesmerizing to me as a kid to watch data moving around on the hard drive and the computer magically getting faster.
Then it would highlight a span of blocks to indicate reading.
Finally it would write those clusters elsewhere, indicating so with a different color.
Edit: Uhh.. and HN deleted my diagrams. See http://pastebin.com/raw.php?i=nKHddiKe