The new Merriam-Webster's Visual Dictionary incorporates 6,000 color illustrations organized by subject area. The full-color pictorial images are grouped into chapters outlining major themes such as:
Plants & gardening
Food & kitchen
Clothing & articles
Arts & architecture
Transport & machinery
Sports & games
The free online access is heavily supported by ads but the medical section may still be useful to patients and students. The links include audio files with pronunciation.
A Dictionary With a Point of View: Announcing Merriam-Webster's Visual Dictionary, Merriam-Webster, 2006.
Netter's Illustrated Human Pathology: A Searchable Collection of Images.
Image source: Merriam-Webster's Visual Dictionary