Here we have an unbiased site with information about car sound systems. There are no products for sale, but there are pages on car speakers with advice for installing car speakers, peventing vibration, fixing speakers and more.
Car Sound System.com also has a page for choosing acar head unit. The brains of your sound system could be a cheap casette receiver or a modern CD receiver.
There’s also a suggestion on using a different car amplifier for both high and low frequency. Of course, speaking of low frequency, the car subwoofer page will help you get that pounding bass.