Check out the New Life Spectrum line of foods. They are guaranteed to improve your fishes' color in ten days, or something like that. Of all the foods I've looked at, NLS had the best ingredients.
Live, freeze-dried, and frozen stuff are pretty good too (in that order
) Hikari and San Francisco Bay make good food in that area and Seachem now has their own line of canned food (shrimp, mealworms, fish eggs and fly larvae).
Personally, it's probably just me, but I stay away from flakes. They lose their nutritious content fairly quickly after being in the water and usually pretty much lose all their nutrition after about six months in the jar.
Most flakes do this, maybe not all, but all the ones I've seen are this way. It's really just a matter of preference.