C++
In Action: Industrial-Strength Programming
Techniques 
C++ In Action: Industrial-Strength
Programming Techniques is a free online C++
book by Bartosz Milewski. The contents are
Introduction, Language, Techniques, Windows
Techniques and Software Project. Source Code
of sample projects is also available.
Thinking
In C++ Second Edition Volume One: Introduction
To Standard C++ 
This is a popular
free C++ book by Bruce Eckel. It covers topics
like Introduction to Objects, Making &
Using Objects, Data Abstraction, Hiding the
Implementation, Initialization & Cleanup,
Function Overloading & Default Arguments,
Operator Overloading, Dynamic Object Creation,
Inheritance & Composition, Polymorphism
& Virtual Functions and Introduction to
Templates.
Thinking
In C++ Second Edition Volume Two: Practical
Programming 
This is a popular
free C++ book by Bruce Eckel and Chuck Allison.
It covers topics like Exception handling,
Strings in depth, Iostreams, Templates in
depth, Runtime type identification, Multiple
inheritance, Design patterns, Concurrency.
Optimizing
C++ 
Free online book Optimizing
C++ provides working programmers and those
who intend to be working programmers with
a practical, real-world approach to program
optimization.
C++:
A Dialog - Programming with C++ Standard Library

This book have free
chapters - Introduction to Programming, Hardware
Fundamentals, Basics of Programming, More
Basics, Functional Literacy, Taking Inventory,
Creating a Homegrown string class, Inheritance,
Polymorphism and etc.