The list here is long: corn (including cornmeal and hominy), rice (white or brown), quinoa, buckwheat (despite the wheat in its name), amaranth, teff, soy, arrowroot, sorghum, tapioca, millet, wild rice, and even glutinous rice (a sticky Asian rice that actually contains no gluten).
Many gluten-free flours are made from the above grains and from foods as diverse as chickpeas, lentils, ground nuts (almonds work well), ground artichoke, beans, chestnuts, and cassava root.
Both grits and its cousin Italian polenta are ground corn and hence gluten-free. Corn flakes are usually gluten-free.
Mexican tortillas are made from corn and are hence gluten-free (unless labeled “flour tortillas”). Mexican tamales are also a corn product. Corn chips and taco chips are often gluten-free, but some use mixtures of corn and wheat flour, so read labels carefully.
Nearly all protein foods, fruits and vegetables are gluten-free, but check for additives. Tofu is gluten-free, unless processed or flavored with wheat-derived soy sauce.