Gluten-Free Ingredients

Gluten-Free Flours

Amaranth
Arrowroot
Buckwheat (it is often combined with wheat flour in pancake mixes)
Corn
Millet
Montina
Potato
Quinoa
Rice
Sorghum
Soy
Tapioca
Teff

Other Gluten-Free Ingredients

Carmel color (in the US this is made from corn)
Citric acid
Dextrin (may in rare cases be made from wheat, but label would say so)
Dextrose
Flavors (may in rare cases be made from wheat, but label would say so)
Glucose syrup
Guar gum
Lecithin
Maltodextrin
Modified food starch (may in rare cases be made from wheat, but label would say so)
Mono and diglycerides
MSG
Vanilla
Vinegar (all except for malt vinegar)
Whey
Yeast (except for brewer's yeast)
Xanthan gum

Note on the food labeling law: Out of the three gluten-containing grains, wheat, rye, and barley, only wheat is required to be listed on labels. Rye will be pretty obvious, but there are a couple of places where barley could pop up such as malt flavorings and malt vinegar.