As long as you go down the route of component's up front and 6x9's in the rear you'll be fine. A lot of people make the mistake of running a sub and 6x9's in the rear shelf, then the sub just batters the 6x9's, so the only effective part of the speaker is the tweeter in the centre.
It's all about budget i'm afraid. You can spend £35-£8000 on component's. It's about matching your speaker's with an adaquate amp. The golden rule to remember is, you can do more damage to a speaker by under powering it than over powering it. Also remember to get speaker's with a high RMS figure, this mean's they can withstand a lot of punishment over a sustained period of time. But make sure the amp you mate with your speaker's hasn't got an RMS figure higher than them, cause they WILL burn out.
Try to use component's that come WITH a crossover, that way you don't need to play around with setting your amp up or using an electronic crossover to control your system.
Some names to look out for are Vibe, Fusion, Rainbow, Audiobahn, Hertz, JBL, Kicker, Infinity.......Don't worry what the speaker grill is like, 9/10 times you'll never use them, you just have to make sure your passenger's are careful with their feet!!!!!!!
Here's a few to tempt you
http://cgi.ebay.co.uk/VIBE-BLACKAIR-6-16-5cm-6-5-2-way-component-speaker_W0QQitemZ260347003823QQihZ016QQcategoryZ18800QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/INFINITY-KAPPA-65-7cs-16-5cm-2-way-component-speaker_W0QQitemZ260347007860QQihZ016QQcategoryZ18800QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/KENWOOD-KFC-S702P-6-5-16-5cm-2-way-component-speakers_W0QQitemZ260347428505QQihZ016QQcategoryZ18800QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/VIBE-SEK-69-6x9-500-Watts-CAR-SPEAKERS-BRAND-NEW_W0QQitemZ250012096183QQihZ015QQcategoryZ14942QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/JBL-GTO-937-GTO-937-300-Watts-6x9-CAR-SPEAKERS-NEW_W0QQitemZ260350056105QQihZ016QQcategoryZ14942QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/INFINITY-KAPPA-693-7i-330Watts-6x9-CAR-SPEAKERS-NEW_W0QQitemZ260349069526QQihZ016QQcategoryZ14942QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/VIBE-SLICK-693-6-x-9-6-x-9-475W-CAR-SPEAKERS-6x9-PAIR_W0QQitemZ260350054645QQihZ016QQcategoryZ14942QQtcZphotoQQcmdZViewItem
http://cgi.ebay.co.uk/VIBE-QB69-3-WAY-600W-Rectangular-6x9-6-x-9-Speakers_W0QQitemZ260347007911QQihZ016QQcategoryZ14942QQtcZphotoQQcmdZViewItem
Amp's are a different kettle of fish, but don't get confused by the figure's that manufacturer's put on their boxes. The ONLY figure your interested in is.....RMS @ 4ohm.
Don't worry about figure's like Total Harmonic Distortion (THD), because you'll only confuse yourself and when it comes to cars it goes straight out the window (literally)
Then you get onto the subject of Soundproofing, Resenance cancelation, Amp wiring kit's, RCA leads.......the list goes on.
If ANYONE wants anymore advice, or anymore info I would love to offer it, but for now......