I have to say that I tried to read the Ethical Slut but it just wasn't doing it for me - the stuff it was talking about just wasn't "my reality", so it was of little use.
I actually found a book called "Open Marriages" by O'Neill to be really helpful. It's not really strictly about polyamory (nor swinging) but it has a ton of the groundwork of what an existing relationship needs to work on in order to make poly work.
"Listen, or your tongue will make you deaf." - Native American Proverb