If you haven't made it to the Natural History Museum's scale exhibit yet, this interactive applet is for you.  And if you have been to the museum lately . . . then you'd REALLY better check this out.  Makes you wish your eyes were electron microscopes, right?  Side note: things like this are pretty much textbooks of the future.  Kids today are so lucky . . 

http://learn.genetics.utah.edu/content/begin/cells/scale/