Online books
Mathematics:
- James Nearing, Mathematical Tools for Physics, Dover Publications, 2010.
- Michael Stone and Paul Goldbart, Mathematics for Physics (also here), Cambridge University Press, 2009.
- Herbert Wilf, Mathematics for the Physical Sciences, Dover Publications, 2006.
- Sean Mauch, Advanced Mathematical Methods for Scientists and Engineers, 2006.
- Eric L. Michelsen, Funky Mathematical Physics Concepts
Dimensional analysis and approximation:
-
Sanjoy Mahajan,
Street-Fighting Mathematics - The Art of Educated Guessing and Opportunistic Problem Solving
The pdf download link hides under the name "Creative Commons Edition"
- Sanjoy Mahajan, Lies and Damn Lies: The Art of Approximation in Science
- Peter Goldreich, Sanjoy Mahajan, Sterl Phinney, Order-of-Magnitude Physics