Reports indicate that the next iPad will have Retina Display instead of the current Super Plane to line switching that's on the iPad 2. Rumours are that the next iPad is being tested currently and previous rumours have indicated a resolution 4 times the amount (2048 x 1536). This is based on the graphics in the latest iOS 5 SDK. The next generation iPad is rumoured to come out this year itself in the Fall, however, given that the next iPhone is also in the works and wasn't announced at this year's WWDC, another iPad this year might really not work out.
The next one will have Retina Display?
Given the warfare between Samsung and Apple, it might be more likely that Samsung might even come out with a tablet with a Retina Display before Apple puts it on their new iPad. Even though Samsung's making the displays for Apple, they might just decide to “keep one for themselves” and launch the next generation Galaxy Tab with Retina Display. The iPad 2, when it came out, was rumoured to have the hi-res display too but the rumours died for several reasons.
Speaking of rumours and what's coming up, there have been some revelations about the next iPhone as well. For starters, the rumour mill says that it is likely to be displayed at Apple's September event where they usually display iPods and music. The 4S will share the iPad 2's dual core A-5 chip and will have a more advanced camera (whether it's more MP or 1080 isn't really revealed).