Rental Car Centres.
Most major airports in USA no longer allow Car Rental companies to have desks in the terminals as they have purpose built Rental Car Centres. The major car rental companies eg Alamo, Avis, Dollar, and Hertz have both their desks and cars in these purpose built buildings. For renters of cars these centres have the benefit of easy access from the terminal, usually by fast people movers (eg Skytrain) and will avoid the central airport congestion. Some locations you will need to get a shuttle bus to the rental car centre. In all cases just follow the airport signage to the car rental desks, at some airports these signs often have a mauve car key symbol.
The list below shows directions at some major airports. These are not the only airports with car rental centres, and the list grows longer every year.
Last edited 09 July 2014 cheap-car-rental.com