Numerical Recipes in Fortran 77  
You can download the each chapter of this free book "Numerical Recipes in FORTRAN 77: The Art of Scientific Computing" in pdf format. Topics include: Solution of Linear Algebraic Equations, Interpolation and Extrapolation, Integration of Functions, Evaluation of Functions, Special Functions, Random Numbers, Sorting, Root Finding and Nonlinear Sets of Equations, Minimization or Maximization of Functions, Eigensystems, Fast Fourier Transform, Fourier and Spectral Applications, Statistical Description of Data, Modeling of Data, Integration of Ordinary Differential Equations, Two Point Boundary Value Problems, Integral Equations and Inverse Theory, Partial Differential Equations, LessNumerical Algorithms. 
Numerical Recipes in Fortran 90  
You can download the each chapter of this free book "Numerical Recipes in Fortran 90: The Art of Scientific Computing" in pdf format. Topics include Introduction to Fortran 90 Language Features, Introduction to Parallel Programming, Numerical Recipes Utility Functions for Fortran 90, Solution of Linear Algebraic Equations, Interpolation and Extrapolation, etc. 
Handbook of Mathematical Functions  
Free book "Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables" by Milton Abramowitz and Irene A. Stegun. 
NonUniform Random Variate Generation  
Free book "NonUniform Random Variate Generation" by Luc Devroye. You can download the each chapter in pdf format. The book presents many practical algorithms on simulation of both discrete and continuous random variables. It also provides with important information on distributions. It is invaluable for a practitioner interested in using densities arising in applications. 
