Interesting. Modern optical microscopes, even cheap ones, do 1000x, though I seem to remember, from playing with a cheapish one, that it was very hard to get a worthwhile image at 1000x. Amazon.co.uk has a microscope for £54.59 that does "1600X" ... "for Kids"! The one I played with wasn't that cheap!

According to random online articles, Antonie van Leeuwenhoek (1632-1723) achieved 275x and a few of his instruments have survived until today, in museums, I presume.