Holiday Cars Direct.com
Providing rentals multiple countries including USA, Spain, UK, Portugal, France and Italy. Online booking available.
http://www.holidaycarsdirect.com

Ofran Holiday Autos
Broker, providing vehicles at many locations worldwide, providing information on destinations and an online reservation system.
http://www.ofran.com/

Skycars
All-inclusive online car hire for the USA, Europe and Australia.
https://www.skycars.com/

RentalCar.com
Worldwide reservations. No online booking.
http://www.rentalcar.com.au/

Car Rental Express
Offers online rentals from independent agencies in many world cities and airport locations.
http://www.carrentalexpress.com/

U.S. Rent A Car
Car hire consolidator offering fully inclusive USA car rental services to UK and European tourists.
http://www.usrentacar.co.uk

CarRentals.com
Offers worldwide service from several suppliers' inventories.
http://www.carrentals.com/

Auto Europe
Provides car rentals, flight tickets, hotels, and specialty cars. Offers prices in a number of currencies. Cellphone hire available to US residents.
http://www.autoeurope.com/

Transhire World Wide
Offers car rentals worldwide.
http://www.transhire.com/

BreezeNet
Online booking of discount rentals at major airports, worldwide.
http://www.bnm.com/

Pinpoint Travel - Car Rental
Find discount car rentals from multiple sites.
http://www.pinpointtravel.com/home?tab=cars