Cars & Light-duty Trucks

ARB Buyer's Guide to Cleaner Cars:   
http://www.driveclean.ca.gov/

CNG vehicles: 
http://www.cngvc.org/ngv/cngvc.nsf/bytitle/infocenter.htm

Alternative Fuel Vehicles: 
http://www1.eere.energy.gov/vehiclesandfuels/

Gasoline Hybrid-Electric Vehicles: 
http://www.nrel.gov/vehiclesandfuels/hev/ and http://www.greenhybrid.com

Compare vehicles side by side at the Web site of US EPA/US DOE: 
http://www.fueleconomy.gov/