Light and Matter by Ben Crowell is a free series of textbooks on general physics.
Applications of Classical Physics by Roger Blandford and Kip Thorne is a grand tour of statistical mechanics, optics, waves, hydrodynamics, plasma physics, and cosmology from a relativistic, geometrical point of view.
In his list of knowledge needed by a good theoretical physicist, the Nobel laureate Gerard ’t Hooft gives links to mathematics and physics textbooks on the Net.
Mathematical physicist John Baez suggests textbooks on the five cornerstones of physics, on general relativity and quantum field theory; and mathematics textbooks for physicists.
TASI (Theoretical Advanced Study Institute) lectures on particle physics and cosmology are good reviews of the subjects.
ASTI: Online Lectures are video and audio recordings of lectures on quantum field theory, particle physics and cosmology by top physicists.
The NIST Reference on Constants, Units, and Uncertainty treats fundamental physical constants, the international system of units, and calculation of uncertainty in measurements.
David Tong: Lectures on Classical Dynamics are lecture notes with many parallels drawn with quantum theory.
Classical Mechanics by John Baez and Derek Wise is a mathematically inclined set of lecture notes.
Structure and Interpretation of Classical Mechanics by Gerald Jay Sussman and Jack Wisdom with Meinhard E. Mayer presents analytic mechanics from a computational point of view, including Scheme code.
Electromagnetic Field Theory by Bo Thidé is a comprehensive textbook that treats hypothetical magnetic charge in addition to standard topics as relativistic electrodynamics. In the appendix, an overview of necessary vector analysis is given. Problems are available separately.
The course by N. David Mermin gives an elementary overview of special relativity by means of thought experiments.
Sean Carroll’s Lecture Notes on General Relativity begins with traditional review of special relativity, considers manifolds, Riemann spacetime geometry, and Einstein equations, applying them to gravitational waves, black holes, and cosmology.
In General Relativity Lectures by Gerard ’t Hooft, a notable application of general relativity is the deduction of the properties of gravitational radiation with Lagrangian method.
In deducing general relativity from first principles in his lecture notes, Matthias Blau takes example by Weinberg, highlighting the principle of equivalence of gravitational and inertial mass. Besides black holes, cosmology and gravitational waves, he treats Kaluza-Klein theories (where the electromagnetic force is reduced to spatial curvature by analogy to gravitation — in fifth dimension).
In an overview, Stefan Waner covers the differential geometry needed for understanding general relativity, and finally discusses black holes.
The 50 page review of quantum mechanics by Niels Walet describes the most important simple quantum systems, introduces basic formalism, and ends with the treatment of the hydrogen atom.
David Mermin describes on quantum computers for computer scientists who have not studied quantum mechanics and for physicists with no education in computer science.
Quantum computing can be learnt from John Preskill’s lecture notes where the whole of quantum mechanics is treated from an information theory point of view.
The article “Statistical Mechanics in a Nutshell” by Jochen Rau summarises the gist of statistical mechanics on twenty-some pages.
Jean Bricmont elucidates chaos, determinism, the arrow of time, entropy, and the rôle of probability in physics in his cogent article “Science of Chaos or Chaos in Science?”. He criticises Ilya Prigogine’s views on irreversibility on the basis of classical works by Laplace and Boltzmann.
Lecture notes on Statistical Physics and Simulation by Franz J. Vesely treat the Monte Carlo method as used in molecular dynamics both for equilibrium and nonequilibrium systems.
Statistical Mechanics of NonEquilibrium Liquids by Denis J. Evans and Gary P. Morriss, first gives an overview of irreversible thermodynamics, classical statistical mechanics, and the Liouville equation. Systems out of equilibrium are treated as perturbed equilibrium systems. Main simulation algorithms are described.
Quantum Field Theory by Mark Srednicki is a lucid modern introduction with focus on renormalization and effective field theory.
The excellent lecture notes Phenomenology of Particle Physics by professor Stephen P. Martin summarize in 250 pages almost all of particle physics, from quantum electrodynamics to quantum chromodynamics, spontaneous symmetry breaking and the Standard Model.
His “Supersymmetry Primer” continues with supersymmetry (breaking), and especially the Minimal Supersymmetric Standard Model (MSSM).
The encyclopaedic textbook Fields by Warren Siegel, ending with supersymmetry, supergravity and string theory, is not a good place to start learning quantum field theory, but the advanced student finds it an invaluable reference.
Superspace, or One thousand and one lessons in supersymmetry by S.J. Gates Jr et al. treats supersymmetry and supergravitation in detail.