Android: We've long said that one of the best ways to find your car is to mark its location on a map before you leave it. Auto Finder simplifies this process by noting where you parked without any input or setup on your part.
Unlike previously mentioned Valet, Auto Finder doesn't require a Bluetooth connection to your car to work (and it's also free, as opposed to $5 with Valet). The app simply detects when you've stopped driving and creates a marker. Drain on battery also appears minimal, so using Auto Finder should be a largely invisible experience until you need it.