(1): Beginner (No or minimal mathematics used. High school level.)
(2): Elementary (Some algebra or basic calculus used. College or first year university module)
(3): Intermediate (Need linear algebra or multivariate calculus. Typical physics major module)
(4): Advanced (Need group theory, tensor calculus or variational calculus. Physics honours level and beyond)
Six Easy Pieces by Richard Feynman Level 1 and 2. A selection of classics by the master!
The Cartoon Guide to Physics by Larry Gonick Level 1. Entertaining and concise.
The Flying Circus of Physics by Jean Walker Level 1. Answers questions related to everyday physics.
Astrophysics for People in a Hurry by Tyson, Neil deGrasse Level 1. Popular.
Principles of Physics by Halliday and Resnick Level 2 Updated Classic.
Concepts of Modern Physics by Arthur Beiser Level 2 and 3. Absolute clarity.
Feynman Lectures on Physics Levels 2 to 4. Classics by the master.
Physics: A Concise Survey of Classical Foundations. Levels 1 and 2.
Real World Mathematics Levels 2 and 3
Reference Handbook of Elementary Mathematics Level 1 and 2
Crash Course in Basic Physics Level 1
High School Physics Course Level 1
College Physics Course Level 2
For the Allure of Physics (MIT Undergraduate Physics Courses) Level 2
Yale Undergraduate Physics Courses Levels 2 and 3
Stanford Undergraduate Physics Courses Levels 2 to 4.
The Theoretical Minimum by Leonard Susskind Levels 2 to 4
MIT Opencourseware. Free in depth courses at Level 2 and above.
A Course in Theoretical Physics Level 2 and above
Hyperphysics. Levels 1 and 2. Concept maps and hyperlinks.
Answers to FAQ's in Physics (Usenet)
Unsolved Problems in Physics (Wikipedia)
Physics Forum Insights (articles)
Physics World (research news update)
Physics. org (research news update)
Hypermaths Basic Mathematics for Physics. Website.
Online Mathematics Courses
Mathematics for Physics Online Lectures
Speculative Physics (Fermilab Videos)
Conversations, Speculations and Controversies (Curt Jaimungal Youtube Channel)
Chats and Opinions (Closer to Truth Channel)
Nobel Laureates in Physics (Video)
Physics in the 20th Century: History and Evolution of Ideas (Online Lectures)
Fall Asleep to Physics 3hr Video
Conservation Laws and Symmetries (Noether's Theorem)
Norton's Dome (Inteterminancy)
Instability of the Solar System (Video Interview)
Instability of the Solar System (Wikipedia)
Chaos Theory (Wikipedia)
Nonlinear Dynamics and Chaos by S Strogatz Level 2 and above (Online Course)