If you plan on staying downtown, in the historic district, walking is easy.

Taxis

When the weather is inclement or if walking too far is difficult, taxis can be very accommodating.  However, don't expect to go out to the curb and hail a cab.  They don't drive around looking for fare in Savannah.  The best thing to do is to get the business card of a company you can call for your cab and they will be more than happy to accommodate you.

However, beware of drivers who give you their personal cards and do not go through a dispatch. You always want to make sure the company is aware of what their employees are doing.

In addition, most taxi's that you take to and from the airport are exclusively for that purpose.  Make sure you ask the driver if that is their only run.

Rental Cars

There is also plenty of free public transportation and tours that will get you around the city conveniently without the worry of trying to find a place to park (not easy).  However, if you want to venture beyond the historic district, a rental car is recommended.