It seems that cornbread is always too crumbly. I have tried adding more eggs and that helps. Also if you are using regular baking powder you should try aluminum free I really like it, here is a link with more info http://www.davidlebovitz.com/2008/10/why-you-should-use-aluminum-free/
I have added mandarin oranges to this recipe, they help with the moisture and also so you don't need to add sugar.
1 cup flour
1 cup cornmeal
1 T baking powder
1/2 t salt
Mix together and set aside
3/4 cup milk
2 T oil
1 small can mandarin oranges drained
Mix wet ingredients well to break up the oranges and mix eggs up.
Add to dry ingredients and mix just until moistened.
Bake in oiled muffin tin until edges are golden being careful not to overcook as this dries them out.