I have been in car audio for a long time now.. still my favorite brand by far is Infinity. The are the makers of
Very expensive home audio speakers and they use the same technology in their car audio stuff. I have a full infinity setup in my car:
6.5" Infinity Kappa Perfect Components up front
2x 12" Infinity Kappa Perfect Subwoofers in the back.
I am pushing everything with JBL amps.
The sound is amazing.
Even with the subs turned off the components are loud as **** and have very good bass response. Zero distortion all the way till redline
Infinity makes 3 lines of speakers based on your budget.
If you shop ebay you can expect these prices
Low end: Infinity Reference ~$110
middle: Infintiy Kappa ~$160
high end: Infinity Kappa Perfect ~$200
These will all sound really good. Its just a matter of how good you want them to sound and how much money you got.
Also a thing to note is the power ratings on these. If you are not going to add external amplifiers, then I would shy away from the Kappas or Perfects and get the reference series.
If REALLY loud and clear is what you want you will need external amplifiers and the Kappas or Perfects.