I have tried and enjoyed some of the baked goods offered by Twins Kitchen (run by two very sweet girls who just happent to be twins), but note that their creations are on the more health-foody side of things.  For example, the delicious icing on  my cupcake had a rather glaze-like consistency and melted easily:   http://www.twinskitchen.com/ 

Another place to consider–though I have not tried this one–is Rosie's Plate in Raleigh: http://www.rosiesplate.com/men…..9th-/cakes 

Finally, if neither of these options work for you, you could pick up a cake mix and frost it yourself with homemade icing or whipped cream.  Powdered sugar is GF, as is butter, and you would just have to be sure to use a GF vanilla (or almond extract, or other favorite flavor). 

Whole Foods's mix would be the cheapest, at around $5 for the mix, but Kroger also has an excellent selection of GF mixes, including Pamela's, which I consider to be one of the best ones out there.  This would be a slightly pricier option than the Whole Foods mix, but Kroger sells the Pamela's icing mix as well, so this would simplify things somewhat if you wanted to go homemade.