Here is a list of online books about Algorithms and Data Structures in various formats available for free :
Advances in Evolutionary Algorithms
by Witold Kosinski, 2008, 284 pages, 40MB, PDF
Advances in Genetic Programming, Vol. 3
edited by L. Spector, W.B. Langdon, U. O’Reilly, P.J. Angeline, 1999, PDF
Algorithmic Algebra
by Bhubaneswar Mishra, 1993, 425 pages, 2.3MB, PDF
Algorithmic Graph Theory
by David Joyner, Minh Van Nguyen, Nathann Cohen, 2010, 105 pages, 760KB, PDF
Algorithmic Information Theory
by Gregory. J. Chaitin, 2003, 236 pages, 0.9MB, PDF
Algorithmic Mathematics
by Leonard Soicher, Franco Vivaldi, 2004, 94 pages, 0.5MB, PDF/PS
Algorithmic Number Theory
by J.P. Buhler, P. Stevenhagen, 2008, 662 pages, PDF
Algorithms
by Robert Sedgewick, Kevin Wayne, 2011
Algorithms
by S. Dasgupta, C. H. Papadimitriou, and U. V. Vazirani, 2006, 336 pages, 2MB, PDF
Algorithms and Data Structures
by Niklaus Wirth, 1985, 179 pages, 1.2MB, PDF
Algorithms and Data Structures for External Memory
by Jeffrey Scott Vitter, 2008, 191 pages, 1.1MB, PDF
Algorithms and Data Structures: The Basic Toolbox
by K. Mehlhorn, P. Sanders, 2008, PDF
Algorithms for Clustering Data
by Anil K. Jain, Richard C. Dubes, 1988, 334 pages, 39MB, PDF
Algorithms for Modular Elliptic Curves
by J. E. Cremona, 1992, 351 pages, PDF
Algorithms: Fundamental Techniques
by Macneil Shonle, Matthew Wilson, Martin Krischik, 2006, 68 pages, 1.2MB, PDF
Average Case Analysis of Algorithms on Sequences
by Wojciech Szpankowski, 2000, PS
Behavior of Algorithms
by Daniel Spielman, 2002, PDF
Categories, Types, and Structures
by Andrea Asperti, Giuseppe Longo, 1991, 300 pages, PDF
Clever Algorithms: Nature-Inspired Programming Recipes
by Jason Brownlee, 2011, 436 pages, 3MB, PDF
Combinatorial Algorithms
by Albert Nijenhuis, Herbert S. Wilf, 1978, 316 pages, 5.5MB, PDF
Combinatorial Algorithms
by Jeff Erickson, 2003, 197 pages, 1.9MB, PDF
Computational and Algorithmic Linear Algebra and n-Dimensional Geometry
by Katta G. Murty, 2001, 554 pages, PDF
Computational Geometry: Methods and Applications
by Jianer Chen, 1996, 227 pages, 1.3MB, PDF
Data Structures
by Dave Mount, 2001, 123 pages, 730 KB, PDF
Data Structures and Algorithm Analysis
by Clifford A. Shaffer, 2012, 613 pp, 2.6MB, PDF
Data Structures and Algorithms
by John Morris, 1998
Design and Analysis of Computer Algorithms
by David M. Mount, 2003, 135 pages, 0.8MB, PDF
The Design of Approximation Algorithms
by D. P. Williamson, D. B. Shmoys, 2010, 496 pages, 2.3MB, PDF
Efficient Algorithms for Sorting and Synchronization
by Andrew Tridgell, 1999, 115 pages, 410KB, PDF
Essentials of Metaheuristics
by Sean Luke, 2009, 233 pages, 5.3MB, PDF
Evolutionary Algorithms
edited by Eisuke Kita, 2011, 584 pages, 30MB, PDF
Evolved to Win
by Moshe Sipper, 2011, 193 pp, 1.9MB, PDF
From Algorithms to Z-Scores: Probabilistic and Statistical Modeling in Computer Science
by Norm Matloff, 2013, 486 pp, 3.4MB, PDF
Genetic Algorithms and Evolutionary Computation
by Adam Marczyk, 2004
Genetic Programming: New Approaches and Successful Applications
edited by Sebastian Ventura, 2012, 284 pp, 6.5MB, PDF
Greedy Algorithms
by Witold Bednorz, 2008, 586 pages, 47MB, PDF
Introduction to Algorithms
by Erik Demaine, Srinivas Devadas, Ronald Rivest, 2008, PDF
Knapsack Problems: Algorithms and Computer Implementations
by Silvano Martello, Paolo Toth, 1990, 308 pages, 23MB, PDF
Lecture Notes on Algorithm Analysis and Computational Complexity
by Ian Parberry, 119 pages, 1.9MB, PDF
Lecture Notes on Bucket Algorithms
by Luc Devroye, 1986, 142 pages, 4MB, PDF
Mathematics for Algorithm and Systems Analysis
by Edward A. Bender, S. Gill Williamson, 2005, 256 pages, PDF
Modern Computer Arithmetic
by Richard P. Brent, Paul Zimmermann, 2009, 239 pages, 1.9MB, PDF
Planning Algorithms
by Steven M. LaValle, 2006, 842 pages, 13.2MB, PDF
Problem Solving with Algorithms and Data Structures Using Python
by Brad Miller, David Ranum, 2011
Problems on Algorithms, 2nd edition
by Ian Parberry, William Gasarch, 2002, 268 pages, 2.4MB, PDF
Quantum Algorithms
by Michele Mosca, 2008, 71 pages, PDF/PS
Quantum algorithms for algebraic problems
by Andrew M. Childs, Wim van Dam, 2008, 52 pages, PDF/PS
Randomized Algorithms
by Wolfgang Merkle, 2001, 46 pp, 370KB, PDF
Search Algorithms and Applications
edited by Nashat Mansour, 2011, 494 pages, 18MB, PDF
Sequential and Parallel Sorting Algorithms
by H. W. Lang, 2000
Sorting and Searching Algorithms: A Cookbook
by Thomas Niemann, 2008, 36 pages, 150KB, PDF
Topics in Theoretical Computer Science: An Algorithmist’s Toolkit
by Jonathan Kelner, 2009, PDF