Randy Cassingham, of This is True, has created a primer on spam. If you already know a little about spam, it probably won’t be of much interest, but it does a good job of summarizing the problem for newcomers. It also has a couple of sections at the bottom discussing chain letters and urban legends.
In the essay, he discusses a point that I’d like to emphasize. You should never buy anything from a spammer, even if the product is something you’d like. A purchase only encourages them, resulting in more spam. If they can’t make money spamming, they’ll stop.