Genesis Chapter 1, Verse 3-4: And God said let there be Light, and there was light. And God saw the light, that it was good: and God divided the light from the darkness.
God didn't create darkness, it was simply there. You can't have one with out the other, as you said, they are two sides to the same coin.
And since "Good" and "Evil" are really just concepts, points of view really, what one person sees as good or evil, is different from what another person says.