I still buy my flours at the grocery store (Hy-Vee). Since it's pretty expensive, I'm in the process of shopping around online to find a better deal. A couple websites I'm checking out are The Gluten Free Mall, Amazon, and Bob's Red Mill.
I buy Bob's Red Mill brand right now, and I'm really happy with it. I trust the brand to be contamination free.
Where do you buy your flours? What brands do you use? I'd love to learn from your experiences!