Georgia State University
Georgia State University: Hyper Physics: Particles
This is a very detailed site containing information on several sub-atomic particles including the Hadron.
Lawrence Berkeley National Laboratory
Berkeley Lab: Particle Adventure: Hadrons, Baryons, and Mesons
This article, part of a particle physics tutorial site, explains and illustrates three kinds of quarks: hadrons, baryons, and mesons.
Other
Stony Brook Center for Nuclear Theory: Nuclear Theory Group
This site describes the ongoing work by the Stony Brook Center for Nuclear Theory in the field of Quantum Chromodynamics, and gives a brief definition of this concept. The site has a link to the webpage of the primary research scientist.