I just recently bough Scientific Soapmaking - it's my reading for the holidays!! I also have Pure Soapmaking, Soap Crafting, and a few others that I can't remember. I'm just getting into making soap for body care (as in, I've been reading, and making for a little over 6 months) - I'm a science nerd, and I really like to know how everything works, so I'm really looking forward to reading Scientific Soapmaking!
Also, if you're planning on selling, I really like the book Good Manufacturing Practices - it's a Canadian author (I"m from Canada), but I feel like it's valuable to anyone in production (I make/sell cleaning products, and love making handmade Christmas gifts, which has lead to my addiction to body care now, lol! That, and moving to hard water land.. I NEEDED something for my drying skin, and options here are very restricted!)