hard question to answer without knowing your budget.
but you'll need for a decent system:
amp wiring kit (atleast 30-40 bucks)
extra speaker wires ($15)
extra power/grounding wires (10)
Subs
Amp for mids/highs
Amp for subs
HeadUnit
and maybe even installation if you dont know how to do it yourself.
some places will install parts if you buy from them.. sometimes free, sometimes for a fee.
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if you're on a tight budget you can get coaxials for the front and rear instead of a component set for the fronts.
tell us how much you're willing to spend for each of these parts.
mid/high amp
sub amp
speakers
Headunit
and we can give better suggestions for your price range.
i suggest checking out ebay for some speakers.. they have really great prices.
you can buy the amp wiring kit from Walmart believe it or not. its just as good as any other amp kit. you'll want to buy a 4 guage amp wiring kit.
for the speaker wires, you can just pop into your local car audio store.
http://www.crutchfield.com/
is a good site to start looking for audio stuff.
but their prices are expensive, so just browse their catalog, but you can find the same items elsewhere cheaper.