Taxis to get around the Amalfi coast are expensive due to the time it takes to travel along the narrow coastal road and return.  Often private hire companies, you can book through your hotel that set a fixed price to travel between two points, can be cheaper than metered taxis.  Example costs as of 2008 are 100 euros from Amalfi to Sorrento, and 70 euros to Salerno. 

Metered taxis will have a taxi sign which lights up when the car is available to hire.  Just hail them by holding up your arm as you would in cities like London or New York City.  The meter will start at around 6-7 euros and the will be small extras for extra passengers, luggage etc.  All restaurants, hotels and bar will be happy to call a taxi for you, but be aware that the meter will start when the taxi leaves to come and pick you up. 

The Amalfi centre has a taxi rank, and drivers will give a business card on request so you can call them again.   Expect to pay around 10-20 euros for journeys across Amalfi, and much more to get to nearby towns and villages.  Service is generally of a high level, with many drivers friendly, and happy to show points of interest along the way

Rental cars are also available. There are big multinationals like Hertz , Avis, Budget , etc.  You can also use a brokerage site, to help consolidate your search:

2. Decodecarhire Milan