We have found the following sources to be valuable in learning about UDL. Some of them are about instructional and curriculum development and others about web usability.

Brown, J. S., Collins, A., & Duguid, P. (1989). Situated cognition and the culture of learning. Educational Researcher, 18, 32-42.

Burgstahler, S. E. & Cory, R. C. (2008). Universal design in higher education: From principles to practice. Cambridge, MA: Harvard Education Press.

Greeno, J. G., Collins, A. M., & Resnick, L. B. (1996). Cognition and learning. In D. C. Berliner & R. C. Calfee (Eds.), Handbook of educational psychology (15-46). New York: Macmillan Library Reference USA.

Keller, J. M. (1987). Development and use of the ARCS model of motivational design. Journal of Instructional Development, 10(3), 2–10.

Mark, M. M., Henry, G. T., & Julnes, G. (2000). Evaluation: An integrated framework for understanding, guiding, and improving public and non-profit policies and programs. San Fransisco: Jossey-Bass.

Merrill, M. D, (2002). First principles of instruction. ETR&D, 50(3).

Morrison, G. R., Ross, S. M. & Kemp, J. E. (2007). Designing effective instruction. Hoboken, NJ: John Wiley & Sons.

Nielsen, J., Tahir, M. (2002) Homepage usability 50 websites deconstructed. Indianapolis: New Riders Press.

Nielsen, J. (1999). Designing web usability: The practice of simplicity. Indianapolis: New Riders Press.

Nielsen, J. (1993). Usability engineering. San Francisco: Morgan Kaufmann.

Norman, D. (1988) The design of everyday things. New York: Currency Doubleday

Reigeluth, C. M. (1999). Instructional design theories and models. Volume II: A new paradigm of instructional theory. Mahwah, NJ: Lawrence Erlbaum Associates.

Schuh, K. L. (2003). Knowledge construction in the learner-centered classroom. Journal of Educational Psychology, 95, 2.

Shneiderman, B. (1987).  Designing the user interface: Strategies for effective human-computer interaction. Addison-Wesley Publishing Company.

Tomlinson, C. A., Kaplan, S. N., Renzulli, J. S., Purcell, J., Leppien, J., Burns, D. (2002). The parallel curriculum. Thousand Oaks, CA: Corwin Press.

Van Duyne, D. K., Landay, J. A., Hong, J. I. (2003). The design of sites. Boston: Addison Wesley.