All Things D, the technology arm of the Wall Street Journal, is reporting that Apple with announce the iPad 3 in the first week of March.
In terms of trustworthiness, the WSJ is the highest on the food chain. Directly below them is Bloomberg, and everyone else falls into the "rumor" category just below that. Some people even think that Apple purposefully leaks information to the WSJ as a way of covertly controlling the PR message. So in terms of rumors, info from the WSJ is the best we ever get.
At this point, I would consider an iPad 3 launch on March 7 as highly likely, with a March 14 backup date for any unforeseen issues. However March 14 strikes me as definitely suboptimal for a launch since the second week in March is typically Spring Break for many schools. Also, we know that SXSW is on March 9th, so they won't compete with that in the news for the launch date. So, I think it will be a March 6th launch, with availability to purchase on March 17th. That way it's announced right before Spring Break and SXSW, and then can build hype in the nerd community during SXSW and build hype in the student community over Spring Break. You couldn't ask for better organic marketing!
We can also say with near certainty that it will have a Retina display, faster processor, and better camera. However, I'm still not convinced it will have 4G LTE compatibility, since the battery drain is still a largely unresolved issue. Bloomberg has reported that it will have 4G LTE, so I'm hoping the WSJ will come out an say the same thing. That would prove it.