GPS device for my Nikon D3100?

I'm looking for a GPS device or attachment for my camera that includes the latitude and longitude, and altitude. I wish to have coordinates for when I leave my normal places of shooting on my metadata so I will know where I was. I'm aware there are some by Nikon but the one I saw had not so great reviews. What should I get?

Go where photography is headed with the Promote GPS! Now photographers can harness GPS technology to pinpoint the precise location from which a photograph is taken. Called "geotagging", this new technology embeds geographic information into a photograph along with the time and date stamp.

You might find something suitable here:
http://www.goughlui.com/?p=1107

I have the GP-1 on my Nikon D90. It has given me excellent results across the USA, Hawaii, Paris, London and Wales.

The only downside that I have found is that when it is in a new area, it sometimes takes a minute or two to sync with the satellites. But once it finds them, it resyncs quickly even if I turn the camera off.

Do be aware that the GP-1 is a battery eater. So, get a backup battery and keep it charged. I was able to use it for 6 to 8 hours of fairly intense shooting in London, so it isn't going to die in an hour or so.