We use code names to name branches and to have an easy way to reference the next version, before Marketing has decided what number or even name to give it when it is officially launched.
I have used names of planets, moons and cities, since they offer an easy successive list to choose from, and have even used names of STDs in an attempt to make sure the business doesn't choose the development code name for the actual release.
Do you do the same? If yes, how do you choose your code names? Which scheme works best, and why? If not, why not?