At one point, we had a Commodore 64 with 64 kilobytes of memory. My father was fond of mentioning that when he was in college, the computer that supported all of CalTech had 64K of memory.
So how would I convey this progression to my children? My iPod shuffle has 1 gigabyte of storage--14 powers of 2 more.
So, I asked, what is something that's 64K now? A pocket watch? A microwave?
My colleagues came up with an answer: 64 kilobytes of memory is the storage used for an icon. (Specifically, a 128x128 icon, using 4 bytes per pixel).
That brings the scale to a comprehensible-enough level to make me say "Wow!"