All of the following grains are gluten-free, and should be so long as the source you are purchasing them from certifies that they are not cross-contaminated by processing on shared equipment (with grains that would contain gluten):
- Buckwheat (it is a fruit technically)
- Quinoa (said "keen-wa")
So, research your options and consider some of these alternative grains. In addition to variety in your diet, you may receive additional health benefits. Here is a link to an article about how Buckwheat May Be Beneficial For Managing Diabetes for example. Some of the other grains I mentioned are quite high in protein (like Quinoa) and high in fiber too (and, dietary fiber can be hard to obtain in sufficient quantities using starches and white-flours -- like potato, corn, rice -- that have been stripped of nearly all fiber).
Follow this link if you would like to read some rather technical information about celiac and gluten free grains according to the USDA. This should satisfy even the most analytical among readers -- especially interesting are the figures toward the bottom of the page that show the genetic relations between various grains and help make clear why certain grains are gluten-free and why others are not (based on family / subfamily of grains).
So, unless someone can offer definitive proof why these other grains are not safe (if pure and uncontaminated by other grains), I think there is plenty of evidence to back up a decision to use such flours in your gluten free and wheat free baking. I suggest that authors of gluten free recipe books do their homework before writing and telling people to avoid these grains also.