A handful of companies are making it a little bit easier to lessen the environmental impact of renting a car. Launched stateside in late 2008, the Australian website VroomVroomVroom.com helps users find low rates on rentals. When you book a car, VroomVroomVroom offsets the rental's carbon emissions, at no extra cost, by making a contribution to the Carbon Neutral Company, which invests in projects such as wind farms. The average donation is $3.32. Kayak.com is getting greener as well; last year, it launched a hybrid filter, which provides the option of searching for only hybrid rentals. One caveat: Some cities, such as New York and Los Angeles, have many hybrids available; others, including Dallas and Hartford, Connecticut, have none. Kayak also lets users search with a miles-per-gallon filter. And at Enterprise Rent-A-Car, customers can pay $1.25 per rental to fund carbon offset projects, and Enterprise matches that dollar for dollar, up to $1 million a year. Enterprise is also outfitting some branches with extra hybrids; for a link to a list of these hybrid-heavy locations, go to www.inc.com/keyword/may09.