In addition to the two great sources Mick suggested, try these on-line journals:
Electronic Journal for Computer, Writing, Rhetoric, and Literacy
http://www.cwrl.utexas.edu/~cwrl/index.html
Journal of Computer Mediated Communication
http://shum.huji.ac.il/jcmc/jcmc.txt.html
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If you're looking for theoretical discussions of rhetoric and technology, here are just a few (most of which are well-known by now):
Haas, Christina. _Writing Technology: Studies on the Materiality of Literacy._ Lawrence Earlbaum Associates 1996.
Landow, George. _Hypertext: the Convergence of Contemporary Critical Theory and Technology._ Johns Hopkins University Press 1992. .
Lanham, Richard. _The Electronic Word: Democracy, Technology, and the Arts._ University of Chicago Press 1993.
Ulmer, Gregory. _Teletheory: Grammatology in the Age of Video._ Routledge
1989.
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This may be far afield, but if you're going to include a section on the "visual literacy/literacies" of hypertext, you might want to look at sources from cognitive science and graphic design:
Low, G.P. "The Rhetoric of Hypermedia: Some rules for Authors." _Journal of Computing in Higher Education_ vol. 1 (1989), pp 39-64.
Marcus, A. _Graphic Design for Electronic Documents and User Interfaces._ Addison-WesleyPublishing Company (ACM Press), 1982.
Tufte, E. R. _The Visual Display of Quantitative Information._ Graphics Press 1983.
White,J.V. _Graphic Design for the Electronic Age._ New York: Watson-Guptill 1988.
Wright, P. "Hypertexts as an Interface for Learners: Some Human Factors
Issues." in _Designing Hypermedia for Learning_, D. Jonassen and H.
Mandl, eds. New York: Springer-Verlag 1990, pp. 169-184.
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And finally, for discussions of rhetorical theories of argumentation as encoded
in database marking, see
J.A.A. Sillence: "Argumentation-Based Indexing for Information Retrieval
from Learned Articles." _Journal of Documentation_ 48 (1992): 387-405.
Best,
Linda
Linda Vavra
LVavra@uic.edu
University of Illinois at Chicago
Co-Moderator, H-Rhetor