Online books, texts, and lecture notes

There are a number of textbooks and lecture notes online. Generally speaking, a great place to start for lecture notes is the arXiv preprint server. Other more general resources are:

• MIT - Open Course Ware Physics
• Gerard 't Hooft - "How to become a GOOD Theoretical Physicist"
• textbookrevolution.org -List of all Physics pages
  
• freescience.info (ebooklist has strong international flavor)
• DC Physics - Online Physics Textbooks
  

Specific notable books include:

• The Basics of MRI (web-book)
  by: Joseph P. Hornak
  very well done and the prototype for what web-books should be
  
• The BaBar Physics Book [SLAC-R-504] (pdf, ps)
  by: The BaBar Collaboration
  a great intro to CP Violation, every HEP exp needs to have a "Physics Book" like this
  
• Advanced Mathematical Methods for Scientists and Engineers (pdf)
  by: Sean Mauch
  aka "Sean's Notes," simply legendary at Caltech for students taking AMa 95
  
• Hyperphysics (web-book)
  by: C. Rod Nave
  another fantastic web-book example
  
• Handbook of Mathematical Functions (web-book w/ scanned jpeg images)
  by: Milton Abramowitz & Irene A. Stegun
  a great reference now with electronic indexing!
  
• Numerical Recipes: The Art of Scientific Computing, 3rd Ed. (pdf) google
  by: W.H. Press, S.A. Teukolsky, W.T. Vetterling, & B.P. Flannery
  sample chapters available for free, full text free for developing countries
  
• Engineering Statistics Handbook (web-book)
  by: NIST/SEMATECH
  a fantastic and pratical web reference for statistical methods
  
• Mathematical Tools for Physics (pdf)
  by: James Nearing
  site includes animations
  
• Quantum Field Theory (pdf) amazon google
  by: Mark Srednicki
  "prepublication draft...contains a number of errors (mostly minor)"
• Lectures on Atomic Physics (pdf) amazon google
  by: Walter R. Johnson
  prepublication draft?
  
• Lectures on Advanced Quantum Mechanics, 2nd Ed. (pdf, ps) amazon google
  by: Freeman Dyson (LaTeX-ed by David Derbes)
  legendary and classic notes that were the de-facto text on QED for several years
  
• Fields (pdf, ps)
  by: W. Siegel
  "first free comprehensive textbook on quantum (and classical) field theory"
• Order of Magnitude Physics (pdf)
  by: Peter Goldreich, Sanjoy Mahajan, & Sterl Phinney
  unofficial book for the popular OOM class at Caltech, partly the PhD thesis of SM
  
• A Radically Modern Approach to Introductory Physics, Vols. 1 & 2 (pdf)
  by: David J. Raymond
  a brilliant idea for freshman physics course: "attempt to develop all of physics in a modern context"
• Motion Mountain (pdf)
  by: Christoph Schiller
  an incredible 1500 page(!) introduction to physics
  
• Essential Physics I (pdf)
  Introduction to Groups, Invariants & Particles (pdf)
  Age of Einstein (pdf)
  by: Frank W.K. Firk
  except AoE, written in the formal style of mathematical texts
  
• Electromagnetic Field Theory (pdf, ps, dvi)
  by: Bo Thidé
  website also includes problem book, "a textbook on the theory of electrodynamics, at roughly the same level as the well-known textbooks by Jackson and Panofsky & Phillips"
• Lecture Notes on General Relativity (pdf) amazon google
  by: Sean M. Carroll
  notes that eventually became the book "Spacetime and Geometry"

I have not included those websites that have illegal scanned copies of books. Writing a textbook takes alot of time & patience and it is just plain wrong to steal an author's hard work.