depends how much money youve got and how mad u wanna go i guess, any sound nut will tell u components and a sub for decent treble, mid and bass.
on the best bang for buck scale tho, personally i dont think u can beat 6x9's, obviously there not as good as the above, but for £50 ish, a fraction of the price of components/amp/sub/wiring kit, and they dont sound crap by any means.