Don't forget your own carmaker's free roadside assistance program. It usually covers new cars and some cover certified-used cars as well, like Ford and Honda. General Motors' assistance program for new cars is good for five years or 100,000 miles. Mercedes-Benz is one of the better ones; its cars get unlimited roadside assistance.

"Manufacturers' programs are quite good," says Reed. "They have a vested interested in making sure the car is treated well, such as preventing towing damage."

According to Edmunds, most of these programs offer essential services, such as towing, lockout help and fuel. However, towing might only take you to the nearest dealer, who may charge more for repairs. Another downside is that the programs eventually end, and some are short -- such as Jeep's three-year or 36,000 mile assistance program.

There's also the GM Motor Club, which covers any make of car. It costs $84 per year for a couple, and offers unlimited towing miles, no limits on service calls and coverage for emergency expenses.