I've had great luck with Crutchfield including things I didn't like but you only have 30 days to do that. You also have to be able to pick out something you like from the beginning.
Good sound is quite subjective but I'll give it a shot.
You should go with separate component speakers in the front, these will have a tweeter that mounts separate from the mid-range driver. You can get away with regular co-axial speakers in the rear. Make sure both sets are the same brand and series. Get an amplifier with 4 channel outputs. Make sure it has enough RMS power output rating to meet the maximum power handling capability of your speakers.
Get a sub woofer, or several. Not so you can vibrate the neighbor hood but o reproduce the bass. For tight, accurate bass get a sealed enclosure. Ported enclosures are louder but not as sonically accurate. Run plenty of amplifier power to your sub.
You will need a crossover to split up the frequencies, some head units have it build in, some don't.
In my Chevy I have a JVC double DIN head unit with Blue-tooth for my phone. It has an external input for my satellite radio receiver and a built in crossover. I put Alpine components in the front doors and Alpine 4 x 6 speakers in the rear doors. These are powered by a 30w RMS x 4 Pioneer amp. I have 2 6.5" Bazooka tubes behind the rear seat powered by a Soundstream amp.
It sounds really good but not that loud. I would like a larger amp than the Pioneer some day but I had it lying around.