Each car has different speaker sizes.
You'll need to find your speaker sizes.
This can be done at
Crutchfield: LCD TV, Car Stereo, Home Theater, Speakers, Digital Cameras
Then you can decide on some speakers.
Since you want clear sound with bass I suggest ~40RMS speakers with a Sony xplod subwoofer.
And two amps how ever you could have 2 after market speakers and bridge the other two channels on the amp and use that for your subwoofer.