Morel and Dynaudio make excellent car audio speakers. Focal are said to be good but I have not heard them. For subs JL Audio are good and also Eclipse.
You will also want a separate amp for your front speakers as the built in amp in the reciever is usually not up to the task of driving quality separates. If you want the best quality sound it's gonna cost you.
As stated by other posters above the car environment is not conducive to really good sound but you can get a pleasing sound even with all the road noise.
I have noticed with newer cars that the stock sound systems are much better than in the past. If your car is newer and sounds pretty good already I would not bother. Maybe just add a sub.
You will also want a separate amp for your front speakers as the built in amp in the reciever is usually not up to the task of driving quality separates. If you want the best quality sound it's gonna cost you.
As stated by other posters above the car environment is not conducive to really good sound but you can get a pleasing sound even with all the road noise.
I have noticed with newer cars that the stock sound systems are much better than in the past. If your car is newer and sounds pretty good already I would not bother. Maybe just add a sub.