Some foods I have found to be extremely good are Ocean Nutrition, Dainichi (by Inochi), New Life Spectrum, Omega One, Hikari Lionhead and Saki-Hikari. I recommend choosing 2 or 3 of these foods so that your goldfish get a more varied diet.
For fresh foods, blanched kale and spinach are decided superfoods. Kale is espescially high in every sort of nutrient... If only I could bring myself to eat it more often! Orange is a good source of Vitamin C and other than that you can try pretty much any fruit or veggie they will eat!
Frozen foods... red wrigglers, bloodworms, krill and tubifex are all good.
You can find gel food recipes on many specialised goldfish forums such as Koko's and the G.A.B. Basically what they consist of is a few ingredients like fresh seafood, fruits, veggies and a multivitamin blended with gelatin and water in a blender and poured out into ice-cube trays to cool. The advantage is that since the food is not baked none of the ingredients lose their nutrients. Also, it is a good way of feeding your fish things normally too small for them to find such as tubifex worms and daphnia.
Until you get your pond I would recommend changing the water very frequently. You can purchase a master test kit so you can monitor toxins like ammonia, nitrite and nitrate and change the water when they get too high. Another motive for changing your water is to encourage growth. All fish secrete a growth-inhibiting hormone into the water. The more of it they sense in the water, the less they grow. In the wild this is useful because if they are in a crowded pond they don't have to eat, and therefore compete for food as much. But in aquariums this effect is drastically amplified to the point where fish actually do in a sense grow to the size of their tanks! Unfortunately their skeletons will 'stunt' but their organs do not, and eventually the fish will die from organ compression. Even minor, non-life threatening stunting is bad news for goldie enthusiasts because the bigger the goldfish, the more beautiful.