Since people here refer to logical fallacies quite a bit, I thought I'd link to some sites that provide definitions and examples of logical fallacies.
The Purdue Online Writing Lab has a pretty good list of the most common fallacies.
The Philosophical Society has a huge list of fallacies.
Finally, the Internet Encyclopedia of Philosophy gives detailed examples and explanations of each fallacy.
List of Logical Fallacies
A list of logical fallacies from various sources