As of my knowledge cutoff in September 2021, here are the top five most expensive cars in the world:

1. Bugatti La Voiture Noire: The Bugatti La Voiture Noire is the most expensive car in the world, with a price tag of $19 million. The car is a one-off custom build, based on the Bugatti Chiron, and features a unique design that pays tribute to Bugatti's iconic Type 57 SC Atlantic.

2. Pagani Huayra BC: The Pagani Huayra BC is a limited edition supercar, with a price tag of around $2.8 million. The car is powered by a twin-turbocharged V12 engine, and features advanced aerodynamics and lightweight materials.

3. Bugatti Centodieci: The Bugatti Centodieci is a limited edition hypercar, with a price tag of around $9 million. The car is based on the Bugatti Chiron, but features a unique design inspired by the classic Bugatti EB110.

4. Mercedes-Benz Maybach Exelero: The Mercedes-Benz Maybach Exelero is a one-off custom build, with a reported price tag of around $8 million. The car was commissioned by Fulda Tires in 2004 as a test vehicle for their high-performance tires, and features a sleek, futuristic design.

5. Koenigsegg CCXR Trevita: The Koenigsegg CCXR Trevita is a limited edition supercar, with a reported price tag of around $4.8 million. The car is powered by a twin-supercharged V8 engine, and features a unique body made entirely of diamond-coated carbon fiber.