Cars & Light-duty Trucks

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

CNG Vehicles:  
http://www.afdc.energy.gov/vehicles/natural_gas.html

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

Gasoline Hybrid-Electric Vehicles:  
http://www.nrel.gov/learning/avf_hybrid_electric.html and http://www.greenhybrid.com

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