LM7805 is an extremely popular and easy to use linear voltage regulator for generating a regulated 5V. It is a easy and simple to use voltage regulator with no external circuitry or components needed for voltage regulation (except for a few smoothing capacitors). It can provide around 500 mA of current without an heatsink and upto 1.5 A with an heat sink.
Note:This regulator has a ~2V linear drop-out. That means you must give it at least 7V to get a clean 5V out.