Physically I believe cars will almost certainly continue to look just like they currently do there seems to be no impetus to make radical changes in the actual appearance of cars. However, there are some fairly radical changes coming to the construction and design of the actual car as a vehicle. Here are some of them which are currently in the prototype stage, and which likely will become commonplace I believe within the next 20 years, Car Trains, Driverless Cars, Night Vision Display.
I believe we will have what some are calling "Car Trains" where cars will have internet connectivity and GPS navigation which will allow cars to communicate with each other and form groups to follow to the same destination. There is a good benefit to this that with this car train it will free up road space and the time it takes to get to your destination because everyone will be moving at the same speed. Also with the minimal distance between cars there will be less traffic congestion on the highway.
Driverless Cars are coming in the near future I think because we already have cars where we can talk to it to call people or set a GPS and things of this nature. A driverless car has already been built and tested by google and the chairman Eric Schmidt has already stated from this test that he believes driverless cars are closer than we think. Some states in the USA have already started implementing the regulations for the driverless car. Night Vision Display in the dashboard is already been done in the high dollar cars, I think before long it will be in every vehicle you can buy.
This will help with the problems of deer and other animal accidents in the middle of the night. This will also help with dark roads with no light to help see upcoming curves or trees close to the road. These are just a few things I see changing in the cars of the future. The only thing that I believe will keep any of this from happening is if the people of today decide they would rather spend time and money on other things like computers, or cell phones. Cars are always changing and now its just a waiting game to get to where these things will be apart of the cars and or lives.