What are the best cars to build into drift cars?

A rear wheel drive car would be the best. This means that when accelerated the back can "flick out" sending the car into a drift. A rear wheel drive car means that is has better handling while drifting as the power is not coming from the front steering wheels.

Some decent models of drift cars are:

Toyota Supra

Scion TC

Nissan 350Z

Nissan Silvia

Mazda RX7

Mazda RX8