Bringuier, J.-C. (1980). Conversations with Jean Piaget. University of Chicago Press (original work published 1977)
Chapman, M. (1988). Constructive evolution: Origins and development of Piaget's thought. Cambridge University Press.
Gallagher, J. M. & Reid, D. K. (Foreword by Piaget & Inhelder) (1981/2002). The Learning Theory of Piaget & Inhelder. Order from online publisher: www.iuniverse.com.
Lourenco, O. & Machado, A. (1996). In defense of Piaget's theory: A reply to 10 common criticisms. Psychological Review, 103(1). 143-164.
Piaget, J. (1964). Six Psychological Studies. New York: Vintage. [the first 70 pages]
Piaget, J. (1973). The child and reality.
Piaget, J. (1983). "Piaget's Theory". In P. Mussen (Ed.) Handbook of child psychology. Wiley.
Piaget, J., & Inhelder, B. (1969). The psychology of the child. New York: Basic Books. (original work published 1966)
Piaget, J. (1985). Equilibration of cognitive structures. University of Chicago Press.
Piaget, J. (1995). Sociological studies. Routledge.
Wadsworth, Barry J. (1989). Piaget's Theory of cognitive and Affective Development (4th edition). New York: Longman.

Biography:

Inhelder, B. (1989). Bärbel Inhelder (Autobiography). In G. Lindzey (Ed.), A history of psychology in autobiography, Vol. 8 (pp. 208-243). Stanford: Stanford University Press.
Piaget, J. (1952). Jean Piaget (Autobiography). In E. G. Boring (Ed.), A history of psychology in autobiography, Vol. 4 (pp. 237-256). Worcester MA: Clark University Press.
Vidal, F. (1994). Piaget before Piaget. Harvard University Press.

General:

Chapman, M. (1988). Constructive evolution. Origins and development of Piaget's thought. Cambridge: Cambridge University Press.

Montangero, J. & Maurice-Naville, D. (1997). Piaget or the advance of knowledge. Mahwah, NJ: Lawrence Erlbaum.

Gruber, H. E., & Vonèche, J. (1995). The essential Piaget. Northvale, NJ: Aronson.

Piaget, J., & Inhelder, B. (1969). The psychology of the child. New York: Basic Books. (original work published 1966).

Piaget and education:

Duckworth, E., Easly, J., Hawkings, D., & Henriques, A. (1990). Science Education. A minds-on approach for the elementary years. Hillsdale, NJ: Lawrence Erlbaum.

Furth, H. (1970). Piaget for teachers. Washington: Prentice Hall.

Kamii, K. (1985). Young children reinvent mathematics. New York: Columbia University Press.

Kamii, K. (1989). Young children continue to reinvent mathematics (2nd grade). New York: Columbia University Press.
The clinical method:
Piaget. J. (1972). The child's conception of the world. Towota, NJ. Littlefield Adams (original work published 1926)

Smith, L. (1992) Judgments and justifications: Criteria for the attribution of children's knowledge in Piagetian research. British Journal of Developmental Psychology, 10 (1-23).

For early childhood people:

DeVries, R. & Kohlberg, L. (1987). Constructivist early education: Overview and comparison with other programs. Washington D.C.: National Association for the Education of Young Children.
DeVries, R. & Zan, B. (1994). Moral classrooms, moral children: Creating a constructivist atmosphere in early education. NY: Teachers College Press.

For everyone:

Ginsburg, H. (1997). Entering the child's mind. NY: Cambridge University Press.
DeLisi, R. & Golbeck, S. (1999). Implications of Piagetian theory for peer learning, (3-37). In A. O'Donnell & A. King (Eds.) Cognitive perspectives on peer learning. Mahwah, NJ: Lawrence Erlbaum Associates.