Hiya Melie. ^^ Everyone has a different opinion on brands for goldfish, but everyone seems to agree that sinking pellet foods are best. I personally like Omega One pellets, but I've also heard good things about Hikari foods and Pro-Gold (PG can only be bought online though).
Also, when feeding it's good to pre-soak food in a cup of tank water to soften and to allow any compacted air to be released.
Aside from a staple pellet diet, I like to feed HBH Spirulina pellets, deshelled peas, and other fresh veggies (broccolli, zucchini, lettuce, spinach, etc). Other members feed live, freeze dried, or frozen bloodworm and brine shrimp. Also spirulina, seaweed, or daphnia flakes, and tons of other fresh vegetables. Some people even give their goldfish fresh fruit every now and then!
There's a big thread floating around somewhere with food people feed their fish, if you want more ideas...
Here:
http://www.kokosgoldfish.invisionzone.com/...hp?showtopic=82Hopefully that helped, and wasn't too much rambling for you! ^^