An easy recipe that I stumbled on somewhere...
1 white or yellow box cake mix
2 large eggs
1/2 cup melted butter
1 cup chocolate chips (or other add-in)
Mix cake mix with melted butter and two eggs with a hand mixer. The batter will be very thick, dont worry, this is the way it is supposed to be. When batter is combines, mix in chocolate chips (or your other alternative).
Using a rubber spatula or scraper, spread batter into an ungreased 9x13 pan.
Bake at 350 degrees for 20-25 minutes. Enjoy!