I used to have some app that would find my car, but now what I do is use Google+ and "Check In" wherever my car is at, or whenever I just want to remember a location (a friends house, etc...) and select at the bottom of the list "Add new location" (or something like that) since this is not a restaurant or any other public place.
I'm sure this is not the way this was meant to be used but it works. I wonder if there is another explicit way to do this with Google+ or Google Maps. I think is very silly that they don't add this feature since it's almost already fully implemented.
I can't find a way to save custom locations to my favorite locations either. Can't find this kind of feature in Google Maps either. I also don't want to install a new app unless is some kind of Google Maps addon, since I already can do this with Google+ the way I described above.