A report from Bloomberg has the next iteration of the iPad on the way as soon as March, with a faster processer, usabiity improvements, and support for next genereation wireless networks.
One of the article's three sources claims that the device is already in production at Asian manufacturing plants, with plans to reach full volume by the next month. The other two confirmed that the iPad 3 will ship with a quad-core chip and "an ehancement that lets users jump more quickly between applications."
Other rumored upgrades include a new HD screen with a higher pixel density and support for LTE wireless networks. LTE support would an be interesting addition, as it would mean Apple would be bringing support for so-called 4G networks to the iPad before the iPhone. The Bloomberg report says the move is intentional, as the iPad's larger battery is better equipped to cope with LTE's increased power requirements.
Per usual, Apple hasn't commented on the rumors.