Argumentation and Critical Decision Making is a textbook I "had" to buy this past semester and it's one of the few I'll keep. It really opened my mind to the argumentation process and honestly I really enjoyed reading it.
My actual class was a total BS, easy A, but if you're looking for a great reference book that's easy to read I would highly recommend it. I've just started my second read of it.
I know.....textbook prices....I'm sorry, but I just had to suggest it.