There are new credits available for the 2009-2010 tax year for installing energy efficient products. Link
One of the credits is for efficient gas water heaters. Another is for electric heat pump water heaters. So far as I know, no major manufacturer makes a standalone, all-in-one heat pump water heater. I have seen heat pump add-ons available for standard electric water heaters, but have not seen a prepackaged kit (with both a storage tank and heat pump).
The problems I see are that this is a relatively untested technology, and that it requires that the water heater be in an open area for the heat pump to operate efficiently (or a vent to the outside). Also, they require a condensation drain, and it's likely that a heat pump will be noisier than a standard water heater (but not as loud as a forced-induction water heater).
In light of the tax credits, are any major manufacturers (e.g., Rheem, Bradford-White) planning to introduce a heat pump water heater?