There are many different type of fats and oils you can use to make soap. Use these links to decide which to use.
As well as having different properties, fats and oils differ greatly in price. While you get a lovely soap from olive oil, it's expensive to purchase the fresh, cold-pressed stuff that you'd usually only use as a salad dressing. You may want to render your own fats from meat (think duck, pig, beef..) or buy bulk oil from a wholesaler. When you buy oils make sure you read the fineprint on the label and check the packaged date - the large print doesn't always tell the full story of what you are buying. All oils should be less than two years old.