What flour is gluten free? (without having 'gluten free' stated in the title)
Unfortunately your options are pretty limited in the way of flour, but all rice flours are fair game, as are tapioca starch and potato starch. Cornmeal is also naturally gluten-free and is a great option for gluten-free baked goods. Oats and oat flour too!
(Watch out for oats and oat flour; unless they're specifically derived from gluten-free oats, they likely have gluten in them from cross-contamination. Most oats are processed on the same equipment as wheat and have enough gluten content to make most people with gluten allergies sick.)
I think your gluten-free flour options aren't really that limited. Amaranth, millet, buckwheat, teff, arrowroot, rice flours, corn/masa, tapioca, potato, coconut, nut flours, garbanzo, other bean- and pea-derived flours--all are naturally gluten-free.
These are good resources for more information:
If you avoid wheat, spelt, kamut, rye, oats (unless labeled/tested gluten free), and barley, all other foods that can be used as grains can be used. It is important to learn all the names that gluten can masquerade as, and use recipes developed by people who are well informed. The websites Syronai give are an excellent place to start. We've found that mixes can be very helpful -- Schar and Gluten Free Pantry are 2 good ones, also Bob's Red Mill for lots of mixes, support ingredients and recipes. Syronai's list points out that it is important to stretch your understanding of what is used as flour -- nuts, beans, seeds, starches are all possibilities.