Leaked iPad parts suggest that the iPad 3 will have a larger battery, an updated camera, and a Retina display all in the same form-factor as the iPad 2.
RepairLabs got its hands on what are said to be insider photos of the the rear-shell of the device, which seems to point to a few changes coming to the next generation of the tablet. The mounts for the iPad's logic board are different and the casing also has space for a larger battery, plus a slightly different camera. The mount for the display is also slightly different, indicating we'll see a change (and hopefully an upgrade) on that front as well.
After looking at the rear casing, RepairLabs source thinks that the iPad 3 will keep the same form-factor as the iPad 2, however, previously rumors have indicated the next-generation of the tablet would be slightly thicker than its predecessor.
Of course, it's all still in the realm of speculation at this stage and without placing the casing beside the iPad 2 it's hard to tell how different the two tablets may be.
The iPad 3 is rumored to coming next month.