Encontrei no site citizen428.net esta excelente lista contendo vários eBooks gratuítos sobre diversas linguagens de programação, material muito bacana para quem está pretendendo ampliar seu conhecimento em linguagens. Abaixo segue a lista contendo 30 eBooks (em inglês):
Lisp:
How to Desing Programs
Let Over Lambda
On Lisp
Practical Common Lisp
Programming in Emacs Lisp
Programming Languages. Application and Interpretation
Structure and Interpretation of Computer Programs
Teach Yourself Scheme in Fixnum Days
Ruby:
Data Structures and Algorithms with Object-Oriented Design Patterns in Ruby
Learn to Program
MacRuby: The Definitive Guide
Programming Ruby
Ruby Best Practices
Javascript:
Building iPhone Apps with HTML, CSS, and JavaScript
Eloquent Javascript
jQuery Fundamentals
Haskell:
Learn You a Haskell for Great Good
Real World Haskell
Erlang:
Concurrent Programming in Erlang
Learn You Some Erlang for Great Good
Python:
Dive into Python
How to Think Like a Computer Scientist – Learning with Python
Smalltalk:
Dynamic Web Development with Seaside
Pharo by Example
Squeak by Example
Diversos:
Algorithms
The Art of Assembly Language
Beginning Perl
The C Book
Compiler Construction
Learn Prolog Now!
Objective-C 2.0 Essentials
Programming Scala
Mundo Tecnológico 