Black Holes - A very thorough introduction, studies the Schwarzschild, Reissner-Nordstrom, and Kerr solutions using a variety of coordinate systems. Additional topics include gravitational collapse, horizons, singularities, Carter-Penrose diagrams (aka conformal compactification), Hawking radiation and black hole thermodynamics
Bondi K-Calculus - A simple derivation of Einstein's theory of relativity which is widely taught to undergraduate physics students. The mathematics required though make this easy for anyone to understand.
Cambridge Relativity - Non-technical descriptions of cosmology, black holes, cosmic strings, inflation, quantum cosmology, and string theory.
Cosmology - This page contains information about the course Cosmology and exobiology read in the fall semester 1999 at the Physics Institute of NTNU, Trondheim
Falling into a Black Hole (Andrew Hamilton) - Fall into a black hole on a real free fall orbit. All distortions of images are real, both general relativistic from the gravitational bending of light, and special relativistic from the near light speed orbit.
General Relativity Tutorial (John Baez) - This is bunch of interconnected web pages that serve as an informal introduction to general relativity. The goal is to demystify general relativity and get across the key ideas without big complicated calculations.
Relativity and Cosmology - undergraduate course notes include both special relativity (e.g., spacetime, Lorentz invariance, various "paradoxes") and general relativity (e.g., equivalence principle, black holes, gravitational waves, experimental tests of gtr). Apparently a survey course for non-majors, with little math but some very nice graphics.
A Short Course on General Relativity - A graduate level course which includes weak field theory, gravitational waves, radiation damping, cosmology, the Friedmann and Lemaitre dusts, singularities, black holes, the Schwarzschild metric and Kruskal's extension of it. This is a single postscript document.
Space, Time, and Cosmology - Website for an online relativity class. Covers special relativity in depth and general relativity at a more qualitative level. Contains tutorial material, references, and links.
Spacetime 101 (Patricia Schwarz) - some basic background covering how mathematical models of space and time have evolved since ancient times, from the Pythagorean Rule to Newtonian mechanics, Special Relativity and General Relativity.
Special Relativity - A set of online lecture notes for a course in special relativity from the University of Winnepeg.
Tensor Calculus and Continuum Mechanics - A free downloadable textbook on introductory tensor analysis and continuum mechanics, in PDF format, from Professor John J. Heinbockel at Old Dominion University.