While the 2004-2008 Prius is the most popular hybrid conversion, it is also possible on 2005-2008 Mercury Mariner and Ford Escape hybrids.

CNN: Hybrids trick out, plug in

In terms of building greener cars, Ford is planning the 2007 Mercury Mariner Hybrid (the regular Mariner is a new companion to the regular Escape) and a hybrid midsize sedan that will follow it.

FORBES: Forbes First Drive: The First American Hybrid

What's to be left seems to be the Mercury Milan, a four-door sedan version of the Ford Fusion, and the Mariner, the Mercury version of the Ford Escape SUV.

FORBES: Magazine Article

Mariner 10, the last spacecraft to visit Mercury, imaged only about 40 percent of the planet, he said.

NPR: NASA Probe Glimpses Unseen Side of Mercury