iPad 3: This iPad could be the iPad 3, a completely new iPad with a retina display and other features we have yet to hear about. But, the only thing wrong with this theory is this picture:

iPad 2 Plus: So that picture suggests that it won't be an iPad 3. Well, what if it's a slightly upgraded version of the iPad 2, just a little thinner, a little lighter and with a retina display, named an "iPad 2 Plus?", similar to the case of the iPhone 3G and the iPhone 3GS? Many analysts are suggesting this theory.
iPad HD: The third theory is that Apple will make a slightly more expensive "iPad HD", an iPad 2 with a retina display and apps such as Final Cut Pro and Aperture, and sell it alongside the iPad 2. This case is more similar to the MacBook and MacBook Pro.
Whatever the name may be, I expect (and hope) that the next iPad will be worth buying, and I certainly will buy it if it is!