I use two all-purpose GF mixes. One is a spin-off of Bette Hagman's recipe:
2 parts brown rice flour
2/3 part potato starch
1/3 part tapioca starch
The other is called three different things: Wendy Wark's flour mix, Multi-blend flour mix, and Karen Robertson's flour mix. It's out of Karen Robertson's book Cooking Gluten-free (which I highly recommend). She has a website with the flour mix recipe on it:
http://www.cookingglutenfree.com/
You can also buy the mix through Authentic Foods (there it is called the Multi-Blend Flour Mix).
I keep both of these made up and in the refrigerator (both have brown rice flour). I think the key to these mixes and all mixes is to use FINELY GROUND rice flours. Authentic Foods sells a finely ground brown rice flour (and white too). Asian stores are cheap places to buy finely ground white rice flour (and sweet or glutenous rice flour).
My local Albertson's now carries Authentic Foods, including the flour mix and brown rice flour. It's cheaper than my health food store.
Esp. with the multi-blend flour mix, I just sub cup for cup. It's great!
Good luck,
Elaine Lambert