The latest Apple rumour doing the rounds? Apple will release a successor to the iPad 2 in March next year. But it won't be the iPad 3; it'll be something else again. You could fill several phone books (remember phone books?) with the output of the Apple rumour industry, so it's worth taking the salt tumbler, ripping the lid off and swallowing the contents whole* before taking in the latest rumour doing the rounds.
Digitimes is the quoted source, noting that the next iPad release will (apparently) be in March 2012, but not a "real" iPad 3. Instead, what we'll see is an iPad that's thinner than the iPad 2, but with better battery life, with the "real" iPad 3 not launching until the 3rd quarter of 2012 at the earliest. If Apple's going to keep with its second generation naming plans, presumably that'd make it the iPad 2s. Still, thinner and better battery life? That's going to take some rather serious engineering if it's true.