MD Rent A Car

If you don't want to rely on public transport (excellent though it is in Sofia) and would prefer to rent a car then a good place to start is MD Rent A Car. They have a good range of cars, from a wee Fiat Panda to the infinitely swanky Alfa Romeo 156, and speak English no problem. If you fancy exploring the Balkans by road then it's possible to take the car out of the country, but extra charges are applicable if so.