Mustangs! No? Maybe pony cars? Get it, because...no? Oh alright fine.
It seems like a broad question, but assuming you want something based on current, existing vehicles, your only real option is an up-fitted, high-roof commercial van.
Why a commercial van? For a few main reasons.
- High roof available to allow the centaur to enter from the back
- Usually truck-chassis-based, to support the weight
- Commonly up-fitted for a variety of duties
Your centaur is, assuming normal human and horse sizes, probably 8-9 feet tall and weighs close to a ton. A normal car is not going to carry 2,000 pounds of driver that's still probably 5 feet tall when they are sitting. A truck-chassis work van could.
The high roof is going to be necessary to allow your centaur to get anywhere close to the driver's position, otherwise you're going to need some sort of conveyor system to get them in place. With a high roof, they can enter through the "trunk" doors, walk up to the front, and then sit.
In addition to the physical size requirements, these types of vans are very frequently outfitted with a variety of add-on equipment for a number of uses. That means third-party up-fitters are used to working with them, and should be able to easily adapt some equipment to meet your centaur's needs.
Since your centaur is going to be "sitting", all-hand controls will be necessary, but that's not a problem. We currently have vehicle hand controls for people without use of their legs.