The following sites have useful information, images and tutorials on fluroecence and other aspects of microscopy.

The Molecular Expressions site contains a plethora of microscopy information, images and tutorials.

MicroscopyU is ran by Nikon. While providing information about Nikon microscopes it also provides detailed information and tutorials about basic microscpy and fluorecence concepts.

The Microscopy Resource Center is ran by Olympus. Like MicroscopyU it provides information about the companies equipment but also has a large collection of tutorials and interative java applets demonstrating microscopy concepts.