The Betty Crocker Gluten Free brownie mix is actually really really good - about 100x better than the Betty Crocker GF chocolate chip cookie mix. The brownies taste just like regular brownies - so much so that my husband even eats them! They are moist and chocolatey and good.
They are available at most regular grocery store chains either in the baking aisle or in the diet foods aisle by the diabetic products. However, watch out for the price because they can run as much as $4.79 per box. I only buy them when they go on sale for about $3 per box. You can buy a set of six boxes from Amazon.com for under $24 with free shipping.