This page collects some online resources that I have found helpful.

• David Malament’s notes on General Relativity are absolutely invaluable. They include the most (only?) systematic treatment of geometrized Newtonian gravitation, using the same conventions that David uses throughout the rest of the book for GR. His other lecture notes, on special relativity and topics related to quantum theory (including Bell’s theorem and quantum logic), are also extremely clear and helpful.
• Bob Geroch has recently compiled a collection of notes and pedagogical materials from a wide variety of courses he has taught over the years. His perspective on these many topics is often eclectic, and always deeply insightful.
• Hans Halvorson’s mathematics for philosophers page contains some great recommendations for foundations-of-physics-oriented mathematics texts, as well as providing a nice picture of how the various pieces of mathematics and mathematical physics fit together.
• Jerrold Marsden, who passed away in 2010, still has a website. It includes links to all of his books, many of which are available online for free. Most notable is his “Foundations of Mechanics”, a classic.
• Fields medalist Alain Connes provides access to both of his massive and fascinating books for free online on his website.
• John Baez’ website is a treasure trove. He has several courses’ worth of lecture notes, plus some of his books available for download. And his little notes on all sorts of topics often contain very deep insights.
• Erik Curiel maintains a collection of physics, philosophy, and mathematics texts that are available online. His taste is eclectic, but impeccable. The site is priceless if only because it is the only place on the internet where one can find so many of Howard Stein’s papers, which should be required reading for everyone.
• Bryan Roberts has compiled a (nearly) complete bibliography of John Earman’s work, including electronic versions of some very hard-to-find books.
• Jeff Barrett, Peter Byrne, and I edited the Everett Papers Project. This archive contains essentially all of Everett’s papers, including many drafts of his dissertation, wherein he first developed his interpretation of quantum mechanics. It is a useful resource for anyone interested in Everett scholarship or the Everett relative-state formulation of quantum mechanics.