PathoPic
PathoPic is a free online image database. This site is a little unique in its way of presentation of data. A search form is used to accurately locate images instead of arranging them in categories. The search criteria include Topography, Stain, Image type ( Histology, Gross, Cytology, Radiology, Frozen Section etc). A description is available with each image to aid in understanding.
Three browser windows/tabs are required to access information from this site. One for search form, one for displaying the search results and the last to view the selected image and its description. If you are confused about the navigation, access the guided tour here.