Mission Critical
http://www.sjsu.edu/depts/itl/
A very useful interactive tutorial for critical thinking from San Jose State University. Lots of exercises and explanations of basic concepts are provided.

The Atheism Web
http://www.infidels.org/news/atheism/logic.html
Even if you don’t agree with the ideology, this is a good and even-handed introduction to informal logic with an extensive list of fallacies, examples, and explanations.

The Critical Thinking Community
http://www.criticalthinking.org
Sponsored by Sonoma State University and intended primarily as a resource for instructors, but contains some valuable information for students too. See the glossary of critical thinking terms in the"library"

The Critical Thinking Web Site
http://www.kcmetro.cc.mo.us/longview/ctac/corenotes.htm#
From Longview Community College, also intended primarily as a resource for teachers, but with a section of excellent explanations of the core concepts of critical thinking, including fallacies

Informal Fallacies
http://www.drury.edu/faculty/Ess/Logic/Informal/Overview.html
An excellent guide to fallacies

Mind Tools
http://www.psychwww.com/mtsite/page2.html
Explanations of problem solving techniques and analytical methods including brainstorming, lateral thinking, and statistical methodology

Guide to the Logical Fallacies
http://www.intrepidsoftware.com/fallacy/toc.htm
Definitions and examples of the standard fallacies taught in critical thinking courses; note that names of the fallacies often vary

Argumentative Writing
http://www.swifty.com/VB/logic/outline.htm
A guide to the use of logic in writing; also covers the basic concepts of informal logic

A Dictionary of Philosophical Terms and Names
http://people.delphi.com/gkemerling/dy/ix1.htm
Entries on concepts in logic and critical thinking, including fallacies

An Introduction to Logic for Liberal Arts and Business Majors

An Introduction to Logic for Liberal Arts and Business Majors
http://www.hofstra.edu/~matscw/logic/logicintro.html
A comprehensive online text with exercises on propositional logic

Propaganda Analysis Home Page
http://carmen.artsci.washington.edu/propaganda/contents.htm
An excellent discussion of propaganda and logical Fallacies using real historical examples. See the Propaganda Gallery, a collection of propaganda film clips.