Souk Mubarakiya has a pretty good gold market and the prices are fairly reasonable. The stores usually give you a good price when selling your gold or you can trade it in on something else because they go by the weight. There's a gold shop in Fahaheel and the guys there will make anything you want just bring a drawing or idea and they'll make it for you and even deliver it for you too.
I had a silver design made for my daughter's birthday and the owner delivered it to me which was cool. They are really nice guys also. Most of the expats I know go there. Here are some pics of the shops in Mubarakiya.