If you want top of the line sound you cant beat a bose. Start with the regular speakers in your car and if you still want more get a amp and some subs (1 or 2) (10 or 12 inches should do you fine) I would recommend Alpine subs and amps if you want to go that route. The sound perfect compared to other systems and give off the perfect bass line.
Since your not trying to spend a arm and a leg, Try getting Kenwood speakers, Pioneers kinda suck. I wouldnt waiste my money on a non name brand. Check out your local walmart see if they have anything you like if not head over to a audio store and talk to them about it.