This is going to get many answers because i think it's a matter of opinion. Me personally, JL Audio is the best out there for sound quality. It depends on what kind of sound you are looking for and what is in your budget. You may be content with a $50.00-$100.00 set of Pioneer or Sony speakers or you may prefer $500.00+ sound more. Best thing to do is take some trips to shops that sell different brands, ask there opinions, listen to the different brands and repeat until you form your own opinion and find what kind of sound you are looking for.
Focal, Rainbow, Hybrid, Image Dynamics, Boston Acoustics, just to name a few.
