To rent a car is a very good alternative to enjoy and visit towns or points of touristic interest located outside Madrid - as Toledo, Aranjuez, El Escorial...)

Main places to rent a car in Madrid are:  Atocha Station (click here) , Chamartín Stantion (click here)  and  Airport (click here)

If you want to rent a car, here you have the sites of the main companies which offer car rental in Madrid

Avis: www.avis.es
Europcar: www.europcar.es
Eascar: www.easycar.es
Hertz: www.hertz.es
Pepecar: www.pepecar.com/

If you want to go form the Airport to Madrid or to Madrid to the Airport There is an airport shuttle service called AresMobile/AeroCity Services:

Airport Shuttle Services:
There is an airport shuttle service called AresMobile/AeroCity Services (www.aresmobile.com) in order to travel from door to door in a cheap and efficient way from your hotel or house to the Barajas Airport. The company has two desks, one in Terminal T1, T2 and T4. It also offers car rental with driver for short journeys and all sorts of services.