Read Recently -- September -- "Logic is a wreath of pretty flowers which smell bad"
With Good Reason: an introduction to informal fallacies sixth edition by S. Morris Engel
I spend enough time on the internet that I have an interest in how to argue well. I still don't think I can do it, but I'm working on it. Having my own copy of Engel's book should help. He spends the first half explaining how logic works in arguments, and the second half explaining the fallacies you can commit (I think there should be a "logical fallacies bingo card"--then you could play along with the more heated arguments).
It isn't a perfect book, mind. The explainations are not always well-written. For example, in the first half of the book he explains Venn Diagrams. Now, I've encountered them around the net, but usually in a less-than-serious fashion. I've never pretended to understand what they were about. Now that I've read Engel's explaination, I still don't understand them but I don't care, either. Also, the book is illustrated with comic strips that Engel uses to provide humourous examples of the fallacies in question; they are accompanied by captions that make him look like he doesn't understand humour at all (I'm sure that was not the intent).
Still, it's nice to have everything gathered in one handy reference. With that in mind, this is mildly recommended.