Lisp/Scheme:
How to Design Programs
Interpreting Lisp (PDF, suggested by Gary Knott)
Let Over Lambda
On Lisp
Practical Common Lisp
Programming in Emacs Lisp
Programming Languages. Application and Interpretation (suggested by Alex Ott)
Structure and Interpretation of Computer Programs
Teach Yourself Scheme in Fixnum Days
Visual LISP Developer’s Bible (suggested by “skatterbrainz”)

Ruby:
Clever Algorithms (suggested by Tales Arvelos)
Data Structures and Algorithms with Object-Oriented Design Patterns in Ruby
Learn Ruby the Hard Way
Learn to Program
MacRuby: The Definitive Guide
Mr. Neighborly’s Humble Little Ruby Book (suggested by tundal45)
Programming Ruby
Read Ruby 1.9
Ruby Best Practices
Ruby on Rails Tutorial Book (suggested by tundal45)

Javascript:
Building iPhone Apps with HTML, CSS, and JavaScript
Eloquent Javascript
jQuery Fundamentals
Mastering Node

Haskell:
Implementing functional languages: a tutorial
Learn You a Haskell for Great Good
Real World Haskell
The Haskell Road to Logic, Maths and Programming

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
Invent Your Own Computer Games with Python (suggested by D)
Learn Python The Hard Way (suggested by Stephen Wyatt Bush)

Smalltalk:
Dynamic Web Development with Seaside
Pharo by Example (based on the next book in this list, suggested by Anonymous)
Squeak by Example

Misc:
Algorithms
The Art of Assembly Language
Beginning Perl
Building Accessible Websites (suggested by Joe Clark)
The C Book
C# Yellow Book (suggested by Joe Wyatt)
Compiler Construction
Dive Into HTML 5 (suggested by @til)
Higher-Order Perl
Impatient Perl
The Implementation of Functional Programming Languages (suggested by “Def”)
An Introduction to R
Learn Prolog Now!
Learning Go
Objective-C 2.0 Essentials
Parsing Techniques (suggested by IronScheme)
Programming Scala
Smooth CoffeeScript
Type Theory and Functional Programming

转自：http://citizen428.net/blog/2010/08/12/30-free-programming-ebooks/