I have an excellent book called Choose the Sex of your baby the natural way by Hazel Chesterman-Phillips. She mentions diet, sperm count, ovulation and timing. It seems from what I've read the most important thing is timing. Apparently male sperm swim faster but die quicker, and female are slower but last longer. She says it is important to know your cycle and when you ovulate. Sex up to one week before ovulation (stopping a day or so before) is supposed to bring a girl as the sperm can live for a week, whereas for a boy it should be on the ovulation day. I haven't tried the method out, but she has had fantastic success with people who have adhered to her methods. Hope this helps.
Michelle, NSW - 9 yr old boy and newborn baby girl