If you are just looking for better sound, and you want it to look stock, just keep the main head unit, and replace the stock speakers in the doors with some infinity kapaa series speakers. That, along with some dynamat around the speakers, will make the music a lot more clear, and will also make it so you can turn it up louder without as much distortion.
If you want to take it a step further, you could get a small self powered subwoofer, like a bazooka tube, or infinity basslink, they dont take up much room and they will make the low frequencies that your door speakers cant make.