Android: Have a tendency to forget where you parked your car? Park Me Right is an Android app that can help you get back to your vehicle, whether you're in a carpark or on the streets.
Once you've parked your car, fire up the app and it will mark your GPS location on Google Maps and save it so you can retrieve it later. You can use coarse or fine GPS to do it, but the latter is more accurate.
When you get back and need to find your car, tap the "Find Car" button, and the app will show you a compass and your car on the same map so you can find it again. If you prefer, you can use an augmented reality view, so you can hold up your phone and see which direction your car is and how far you have until you reach it.
The app is free and even has its own tool to help you find parking spaces built-in, but I found it a bit spotty when I tested it. The real utility here is the ability to find your car quickly when you're tired or forgetful.