Well go figure. Both CWs used Pamela's GF chocolate cake mix. They said unless you do a ton of GF baking its much easier and cheaper to just find a good mix and use that.
If you want to try from scratch though, check out Manini's. They are a local company that does GF flours and pastas (their fresh pasta is AMAZING!! I would never guess it was GF) and their website has some cake/cupcake recipes. I buy the pasta at Whole Foods, and I think PCC carries their stuff too.