Depending on how much current you need, a 7805 is good for up to 1.0 A but depending on the manufacturer some claim 1.5A. There are also 5 V regulators that are higher current ( 3-4 amps) at a higher cost. The important things to remember is proper filtering and heatsinking. As far as filtering goes, use a 1000 uf 35V electrolytic capacitor on the input and a 10 uf 25V electrolytic capacitor in parallel with a 0.1 uF mylar capacitor on the output. This combination will provide noise filtering and kill any oscillations that can occur. As far as heatsinking goes, the case of the regulator is connected to the ground terminal anyway so no insulating washer is needed. A commercal heatsink can be used or a piece of aluminum 1/8" thick about 10 sq inches. To get an idea of the maximum power dissipation - use 14.4V - 5v X output current ( say 1 Amp ) =9.4 watts. Always choose a larger heatsink, on cool days it won't matter, but on summer days the regulator will run hotter due to higher ambient air temperature and you won't the regulator to thermally shut down. Mounting the heat sink to metal on the car will help sink away some of the heat. No insulating washer is required for a 7805 or equiv. since the tab is connected to it's ground lead anyway. In automotive applications, always make sure that the body ground ( wire from batt "-" to inner fender ) is intact and in good condition, this will reduce headaches with noise and voltage fluctuations when accessories, headlights, wipers etc. are turned on. Search 7805 on google , or go to TI ( Texas Instruments ), National Semiconductor, or Motorola for data sheets and optional devices.