According to All Things Digital (ATD), Apple will announce the iPad 2 on March 2. The site is part of the Wall Street Journal digital network, and the WSJ has the reputation of being one of Apple's favourite outlets for leaking information that it isn't ready to officially announce.
The story cites "several sources close to the situation" but does not name them.
On the other hand, multiple media outlets (eg, Businessweek) are reporting an analyst's assertion that "production bottlenecks" at Hon Hai (Apple's contract manufacturer) may delay shipments of the iPad 2 until June. The delays supposedly relate to recent design changes made by Apple.
Another theory (eg, Forbes) predicts an April release.