Though the Gluten Intolerance Group has a very nice website, the Gluten-Free Registry at http://www.glutenfreeregistry.com/index.jsp has a much more extensive listing of restaurants, plus it's searchable by city and state, as well as by zip code.
Gluten-Free Registry also lists grocery stores with GF sections, caterers, and bakeries. Woo-hoo!
They also have a mini-site for mobile phone reference: http://gfregistry.mobi/
You can even download GPS info directly onto your GPS system: http://www.glutenfreeregistry.com/order-gps-download.do
Now that's a FANTASTIC resource.