The best site I have found to locate the latitude/longitude values is http://mapki.com/getLonLat.php  

You can always find lat/long values by going to maps.google.com and doing a search.  Once you find your location, you can click on the 'Link to this page'.  The URL on the top changes at that time.  You can inspect the URL and find the values by the &ll={latitude},{longitude}.

Or ...

You can use tools like http://www.earthtools.org/