I'll make thing simple for you if your looking for loud and clean on a moderate budget.
Speakers: I'd recommend a component system for the front so that you not left with an absurd amount of bass in the rear with nothing to equalize the sound stage in the front.
I'd personally recommend Polk Audio.
As for amplifiers, if you looking to squeeze the your budget go with a decent set of Kenwood amps, definitely definitely, use a dedicated amplifiers for your 4 main channels, the amplifiers built into head units are usually sub-par and don't really have the firepower (or clarity) one needs to attain decent (>90 db) audio levels.
I would recommend the digital Alpine amps. In particular this
one. This will power the polk audio speakers 10x better than a head-unit and really bring them to life.
The Alpine fx and mrx series are a hybrid of their most popular analog amps and the competition level amplifiers which sell for booku money.
As for a subwoofer? I would steer clear of any of the big name "car audio" brands (ie: Kicker, Pioneer, MTX,etc) The one brand that I can vouch for is Alpine's type-r series.
I would suggest going to
www.partsexpress.com and choosing a high fidelity 10" or 12". truthfully, anything over 300w rms is simply overkill. And make sure you pay attention to the RMS rating NOT the peak rating! Rms power is actual continuous power peak or simply how much of a burst (peak) input a speaker can take.
Your subwoofer options are up to you, but no matter waht you do if you're going to put some "bump in the trunk" please, please, please dynamat the trunk so it's not a rattle bucket, this annoys me greatly and will probably annoy you just as well when you can't enjoy your music over the car rattling.
-Josh
