Under "golden nuggets" there is a whole thread dedicated to suggested reading.
There's a wealth of reading to do there.
I preferred the book "love without limits" by Deborah Anapol
Others frequently site the books Ethical Slut-don't know authors and Opening Up by Tristan Taoromino
Opening up was great for coming up with topics to discuss before embarking-but I don't care for Ethical Slut myself.