References
On-line Sources
http://aleph0.clarku.edu/~djoyce/java/elements/elements.html Euclid's Elements - the text, illustrated via Java applets - a web site developed by David Joyce, of Clark University.
http://www.geom.umn.edu/ The Geometry Center - a mathematics research and education center at the University of Minnesota, funded by the National Science Foundation as part of the Science and Technology Center program; a wealth of information about and software to support and illustrate mathematics.
http://www.perseus.tufts.edu/ The Perseus Project - a work in progress, at Tufts University, but already an immense digital library of resources for studying the ancient world; the library's materials include ancient texts and translations, philological tools, maps, illustrated art catalogs, etc.; among the materials is a complete text copy of Euclid's Elements with Heath's extensive commentary.
http://riceinfo.rice.edu/projects/NonEuclid/ NonEuclid -a web site developed by Joel Castellanos, Joe Dan Austin, and Ervan Darnell of Rice University; a software simulation (available via download) offers straightedge and compass constructions in hyperbolic geometry -- more polished, but not as versatile as "The Lobachevskian Plane".
Books and ArticlesBonola, Roberto. Non-Euclidean Geometry: A Critical and Historical Study of Its Development, translated by H. S. Carslaw, 1911. Dover (reprint), 1955. A classic, thorough treatment of Lobachevskian Geometry, but not easy reading; includes translations of Janos Bolyai's Absolute Science of Space and Lobachevsky's Geometrical Researches on the Theory of Parallels.
Castellanos, Joel, Joe Dan Austin, Ervan Darnell, and Maria Estrada. "An Empirical Exploration of the Poincaré Model for Hyperbolic Geometry", in Mathematics and Computer Education, pp. 51-68, (winter 1993), Volume 27, number 1.
Davis, Donald M. The Nature and Power of Mathematics. Princeton University Press, 1993. Non-Euclidean Geometry is only part of this book, but it touches more explicitly than most on the connection with the theory of relativity.
Gans, David. An Introduction to Non-Euclidean Geometry. Academic Press, 1973. The title is accurate.
Greenberg, Marvin. Euclidean and Non-Euclidean Geometry: Development and History. W. H. Freeman, 1980. Well organized treatment of neutral or absolute geometry, following Hilbert's organization.
Heath, Thomas L. The Thirteen Books of Euclid's Elements. Dover (reprint), 1956. The classic translation of Euclid.
Kline, Morris. Mathematical Thought from Ancient to Modern Times, Chapter 36. Oxford University Press, 1972. A thorough and concise history.
Penrose, Roger. "The Geometry of the Universe," in L.A. Steen's Mathematics Today: Twelve Informal Essays. Springer-Verlag, 1962. Treats the classical non-Euclidean geometries only briefly, focusing on what physical theories suggest about geometry.
Prenowitz, Walter, and Meyer Jordan. Basic Concepts of Geometry, 1965. Ardsley House (reprint), 1990. A very accessible treatment of the basics of Lobachevskian Geometry.
Stahl, Saul. The Poincaré Half-Plane: A Gateway to Modern Geometry. Jones and Bartlett Publishers, Inc., 1993. A thorough treatment of the Poincaré half-plane model and the closely related unit disk model, but technically demanding in its detail.
Trudeau, Richard. The Non-Euclidean Revolution. Birkhaüser Boston, 1987. A well-written coverage of non-Euclidean Geometry with good treatment of history, philosophy, psychology; contains an excellent bibliography for more detailed study.