This is the closest health food store to my house, so I use it quite a lot. It's not cheap (health food stores generally aren't) and it doesn't have the range of some larger stores, but they do a good range of gluten free products and will order items in for you if you know what you're looking for. They even have a range of frozen dessert items that are good for the dairy and gluten intolerant, including cakes and slices.

I was searching for some fresh peanuts that I could crush to make my own peanut butter. Imagine my delight when the staff told me that if I chose the peanuts they would crush them in the shop while I waited. I've never had to crush peanuts again, wonderful.