You have a few options that you could use. It all depends on what you are trying to do with your application. Is this something you want to produce or is this something you are working with at home?

You could use a Zener diode rated at 5 volts. A zener is used to clamp the voltage.
You could make a voltage divider and by selecting the correct resistor values get an output voltage of 5V.
You could use a diode in series with your batteries, not a bad idea as it will give you polarity protection. This should drop the input voltage down by 0.7V.
You could purchase a low dropout voltage regulator. They are alittle more costly than standard voltage regulator. You can find them labeled as LDO's. Take a look on digikey.com and see what you can find.