Here, a photo of an iPad 3 dock connector has been leaked online. Apple.pro has published this photo as what it looks like the dock connector and also a ribbon cable for the upcoming iPad.
MacRumors reports that there are no guarantees that the part depicted in the photos is indeed a genuine dock connector for the iPad 3 as claimed, but the part carries a very similar form factor to the existing part and a part number updated from 821-1180-A in the iPad 2 to a newer 821-1259-06.
The site also reports about the tail end of the ribbon cable which creates a 90-degree turn in this newest part, but the ribbon cable in iPad 2 is totally straight. The site also notices that purported part is white whereas iPad 2 is black. People are claiming that new white connector reveal a customized design.
According to rumors, a high resolution iPad 3 or iPad 2 HD will be release later this year.