Florida State University
Florida State University: Virtual Microscopy
These interactive tutorials allow you to adjust the magnification and focus of the object. Requires Java.
Florida State University
Florida State University: Translational Microscopy
With this interactive tutorial, you can view cholesterol, pesticide, ibuprofen, and other samples under a microscope. You can adjust the focus, intensity, and zoom in on the object. Requires Java.
Other
Science Stock Photography
This site has numerous pictures of microscopic images. It also has a search engine so you can find specific objects. Images were captured with light microscopes, as well as electron microscopes.
Lawrence Berkeley National Laboratory
Berkeley Lab: Ncem: Electron Micrographs
This site contains a gallery of scanning electron micrographs of non living substance.