The only sure way to know the gender of your baby prior to birth is through invasive medical test called a chorionic villus sampling test. These tests are not done for the sole purpose of determining the gender of the baby; but if the there is a medical reason for the test, the doctor will also determine its gender if the parents wish to know. Other medical procedures that may predict the gender are ultrasound tests. This test is not always accurate which depends on the skill of the technician and the quality of the machine.
If you are truly comfortable with whatever gender your baby will be, it's sometimes fun, especially at baby showers, to try and predict the gender of your baby. There are several wives tales' that claim to be able to predict the gender of your baby. Some include the Drano test; how high or low you carry the baby; whether you had a girl or boy before and how different or alike this pregnancy is to that one; and, how often and what time of day baby is most active. Obviously, none of these can be completely accurate and are simply guesses.
Apparently there is an ancient Chinese gender chart that claims to be 90% accurate in determing gender prior to birth if used accurately. The Chinese calendar is very interesting and very unlike western calendars. There are some precise things that have to be done to rely on the Chinese chart, and any results should be taken lightly and in the same context as wives tales.
It's impossible to accurately predict your baby's gender without medical intervention. But it's very entertaining to use various methods to do so and to see if each method brings the same results. Now that may, in fact, be interesting.