I would also advise to stay away from castor oil. It is not that flash for you or bubs if it doesnt work.
I am also looking at natural induction methods and am going to do a post here in a minute. I am actually booked in for acupuncture next Thursday and I will be just over 38 weeks at that point. I have heard it has a very high success rate (88%) of bringing a woman into labour after 1/2 or 3 sessions (usually one or 2 can be enough). I am pretty aware though that if bubs isnt ready nothing will work.
Hope that you can avoid being induced medically and get to go into labour on your own.
Good luck!
Lisa