There have been a lot of threads on this such as
You can find more by using the search facility.
If you were more specific with the type of car and how you want to use the scooter (around town or cross country) people will be able to help more.
I use a supascooter who have quite a range to suit different conditions. As well as folding they split into parts.
While buying online may be cheaper finding a good dealer so you can try it out and check the fit and practicality of putting it in and out of the car is my advice.