These micrographs are from "The Internet Pathology Laboratory for Medical Education" at the University of Utah Medical school. Click here to see additional micrographs of islets at this excellent site.

Normal islet stained for insulin (right) and glucagon (left):

Normal islet:

Islet under attack by immune system:

There are lots of other sites about islets on the web that you can find with a web browser. A couple of the higher quality ones I have found:

Islet with amyloid plaque (typical of type II diabetes)

A lecture on the endocrine pancreas and pancreatic hormones by Prof. D. A. Walsh of the University of California Davis.