BoingBoing published a neat article that says that serious scientists love an $89 toy microscope that you can purchase from Amazon.com and a number of other on-line retailers. (Note that the price at Amazon is quite a bit less than $89.)
The QX5 Computer Microscope from Prima Creations has been uses successfully by Andrew Westphal, an astrophysicist at the Space Sciences Laboratory at the University of California at Berkeley. He reportedly said that a more sophisticated microscope's lens would have been damaged by the acid that's used to separate particles of microscopic space dust.
It's amazing that a device like this is sold as a toy for kids. I want one.