I have one, mostly-healthy basic muffin recipe that I use for most of my muffins:
1/2 cup white flour
1/2 cup whole wheat flour
1/2 cup quick oats
1/3 cup sugar
2 tsp. baking powder
1/2 tsp. salt
Mix these together. (Sometimes I will make up several batches of this at a time and put them in zip-lock bags and have my own muffin mix.)
Mix together separately:
1 egg, lightly beaten
1/2 cup milk
1/4 cup vegetable oil
Add this to the dry ingredients and stir until just moistened.
Now it's time to get creative. You can add any number of things to this: blueberries, strawberries, cherries, chopped apples, nuts, raisins or other dried fruit, cranberries, chocolate chips, flax seeds, orange or lemon zest, etc. Combinations are also good, like chocolate chip-cherry.
You can also add a little cocoa to the dry ingredients to make them chocolate, or some flavor extract. A little cinnamon or nutmeg spices them up, or I replace half of the milk with orange juice to make cranberry-orange-nut muffins.
Fill greased or lined muffin cups 2/3 full. Bake at 400° for 20-25 minutes. This makes 10-12, depending on how much you add to it.
Yummy!