A good quality pellet food is best for goldies; especially fancies, as they can get bloated if they take in to much air eating flake from the surface.
They'll also enjoy bloodworm, daphnia, mosquito larvae (you can catch live ones if you have a water butt in your garden) which you can buy frozen at your LFS and lightly cooked, shelled peas are very good for their digestion and should be feed once a week.
You should also not feed them one day a weeks as this will keep their digestive systems in good order.
Are your goldies in a tank or a pond?