I have not found a prepared mac & cheese that I like. I do really like this recipe from glutenfreeda.com. This site has tons of great gluten free recipes, you should check it out. I usually double the batch and freeze the left overs in portions just right for my son. Then I use them for a quick lunch, or like tonight when we're invited to a barbecue and I'm unsure of the gluten status of side dishes. (He'd much rather have mac & cheese than potato salad anyway.

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Macaroni & Cheese
Servings: Makes 4 servings.
Difficulty: Easy Ingredients
2 Tablespoon butter, (1 Tablespoon reserved for topping)
2 Tablespoon gluten-free bread flour
3/4 cup milk
1/8 teaspoon dry mustard
1/4 teaspoon kosher salt
1 cup cheddar cheese, grated (plus 1/4 cup for topping)
2 cups dry gluten-free rice macaroni noodles or spirals
Directions
Preheat oven to 350ºF.
Melt 1 tablespoon butter in a 1 quart saucepan, over medium heat. Add gluten-free flour and stir until combined with butter. Gradually stir in 3/4 cup milk. Whisk constantly to blend. Cook over medium heat until thickened, stirring constantly. Once thickened, remove from heat and add 1 cup cheddar cheese. Mix well until cheese has completely melted. Add dry mustard and salt. Mix well.
Meanwhile, bring a large stockpot of salted water to a boil. Add gluten-free macaroni noodles. Cook about 10-12 minutes or until noodles are al dente (make sure not to overcook). Drain and rinse noodles.
In an oven-proof casserole, pour cheese sauce over noodles and mix well. Top with 1/4 cup grated cheddar cheese. Bake 30 minutes. Allow to cool slightly and serve.