Kelley Blue Book
Full featured and fast loading site you can use to check prices and other information on a new or used car. Also offers photos, advice and car comparsion when shopping for a car. Price information also available in Spanish.
Fueleconomy.gov features fuel-economy, emissions, and safety data for new and used cars, as well as fuel-saving tips. You can compare new and used cars according to gas mileage, greenhouse gas emissions, air-pollution ratings, and safety records. Internal search engine allows for a quick search.
Safercar.gov is a part of the National Highway Traffic Safety Administration (NHTSA). Featuring the results of safety tests of various automobiles, the site allows buyers to evaluate the anticipated behavior of an automobile in a crash as well as many guidelines for drivers. The site is searchable.
CarRentals.com features a list of low base rates at airports around the country and internationally. This site allows you to make, modify or cancel reservation online. Another useful feature lists the best rental rates updated hourly and it's searchable.