My setup is a JVC Headunit that interfaces with my iPod and iPhone, 2 JBL amps (a 4-channel running doir speakers and a monoblock running the sub), Focal component speakers in the doors, and a Kicker 12 inch in the boot.
Built it up slowly bit by bit cos of the cost but remember that your sound system is as good as your worst component.
I might not have the best system ever, but it's pretty decent
Mine is similar to the above; alpine IDA-X100 headunit, to a HXA-700 signal processor. 4 channel amp and bridged amp for sub. Focal ps165 component speakers for front doors, PC130 speakers for rears and a JL 12" ported subwedge. Sound deaden where appropriate and it sounds awesome! However does cost roughly £1K for the kit...
Seriously, i can't recommend the PS165s enough. if you are on a budget, just wire in a pair of RCAs to the standard HU, a single amp and those components. You'll see an improvement straight off!
All I want is to replace the speaks in the original fittings, I've seen some cheap pioneer ones and then place a 6.5" sub in my parcel shelf, but that would mean id have to buy an amp and I don't want to spend over 100 for it all that's the problem
Could just get a decent stereo and a big sub, that's what ive done, edge 2 x 12 inch in the boot, jvc stereo, no changes to door speakers, sounds perfect