I've currently got a Pioneer deck with Alpine speakers/amp/sub setup.
Here's a list of what they are
Deck: Pioneer DEH-P800BT
Fronts: Alpine SPR-17S Type-R 6-1/2" Component 2-Way Speaker
Rears: Alpine SPR-17C Type-R 6-1/2" Coaxial 2-Way Speaker
Amp: Alpine MRP-M500
Sub: Alpine SWR-1242D Type-R 12"
I would suggest you go high quality front speakers, as you want clear music right? Maybe get a 10" sub depending how much doof doof you want hehe..
Rear's aren't a problem like Shiraz said, don't get splits for the rear... complete waste as you listen to the front mainly!
There's a few good mono amps around, you can get a 4channel and bridge it... but that's kind of a waste in any case... I just got that amp cause it was kinda shoved in my face at the time (ended up having to swap the sub cause they gave me the wrong sub...)
Shop around a bit and ask if any friends work at like JB hifi or something, can get you some good bargains i know i saved hundreds!!!!
Hell if you wanted to, just get a good deck, and really really good fronts (get meh rear's) and just tune it correctly, can get you enough bass/good quality sound did for me for ages! haha