For gluten-free bakers, a combination of brown rice flour, white rice flour, potato starch and tapioca starch makes an excellent substitution for all-purpose flour. These ingredients are available at specialty and natural food markets and from kingarthurflour.com. Coconut flour is also a healthy, gluten-free alternative to wheat and other grain flours. It is very high in fiber and a good source of protein. It’s available at bobsredmill.com.