Merriam-Webster
Merriam Webster: Dictionary Illustration: Respiratory System
Simple labeled diagram of the parts of the human respiratory system.
San Diego State University
San Diego State: Avian Respiratory System and Anatomy
Resource provides two good diagrams of a bird's respiratory system.
University of Minnesota
University of Minnesota: Anatomy Image Bank
Hundreds of anatomy diagrams for classroom or medical use. Each image represented is a simple black-and-white professional drawing of a specific part of the human body.
University of Utah
University of Utah: Cardiovascular Pathology Index
This site features a detailed index of photographs for cardiovascular pathology. You can see what a normal human heart looks like and what a sick one looks like too. Come and check it out.