Kaiser, Peter K.  
   Joy of Visual Perception. An on-line book on the anatomy & physiology of vision, and on visual psychophysics.
   http://www.yorku.ca/eye/

Aristotle  
   De Anima [On the Soul]. One of the first western statements on psychology, and still influential. Full text on-line.
   http://classics.mit.edu/Aristotle/soul.html

Gibson, James J.  
   Purple Perils. A collection of Gibson's private notes for seminars from 1954 to 1979, available on-line.
   http://lor.trincoll.edu/~psyc/perils/

How Brains Think  
   William H. Calvin's 1996 book on evolution of consciousness, intelligence, and language.
   http://faculty.washington.edu/wcalvin/bk8/

Baldwin, James M.  
   Mental Development in the Child and the Race. "Represents a pioneer effort to present a picture of the social nature of the self and the manner of its growth," by one of the founders of American psychology. Full text on-line.
   http://spartan.ac.brocku.ca/%7Elward/baldwin/Baldwin_1906/Baldwin_1906_toc.html

Chalmers, David  
   The Conscious Mind (Oxford Univ. Press, 1996). An interesting monograph on consciousness by a philosopher who believes that a materialistic reduction of consciousness is impossible.
   http://www.u.arizona.edu/~chalmers/book/tcm.html

Berkeley, George  
   A Treatise Concerning the Principles of Human Knowledge. An important work in the history of empiricism and idealism, and a string influence on David Hume. Full text on-line.
   http://www.iep.utm.edu/b/berkeley.htm