O.K Im guessing you want to start from scratch so thats what ill do. First for your head-unit I would reccomend the Alpine 9823. The CDA-9823 has two sets of preamp outputs and its amp is 18 watts X 4 RMS. Next for the front speakers I would reccomend Boston's FS50 component set. Your original door opening is 6 3/4 but these smaller speakers will be easier for your head-unit to power. If you dont want component speakers (speakers that come with a tweeter that is seperate from the woofer and a seperate crossover for the speakers) then I would look at either Boston's FX5 or (the better, but more expensive) NX 57. You might also want to look at JL Audio's TR line of speakers and component sets. For the rear speakers I would look again look at Boston's FX5 or NX 57 speakers. If you want some more power if you buy the NX57 speakers and the component sets (not the lower priced speakers) then look at an external amp like the Alpine MRP-F240 or the Rockford Fosgate Punch 301X. These amps will power your speakers much more easily then your head-unit would and makes them sound better.
For small subs that sound good I would look at JL's W3v2 10" subs or there W0 10" subs. Either of these will be good for sound quality and dont cost too much. the W0 10" sub is around $129.00 I think and the W3v2 is around $179.00 or so. If you buy two of the W3v2 subs the get them in 4 ohm dvc, if you buy only one then get it in 2 ohm dvc. An amp for one W3v2 would be the Rockford Fosgate Punch P301 which does 300 watts RMS when bridged into 4 ohms. For two W3v2 10" subs a Rockford Fosgate Power 551S would output 550 watts RMS in 4 ohms bridged. Now if you buy one of the W0 10" subs then I would get something like the US Acoustics USB-600D amp which would give that sub 200 watts RMS in 4 ohms. For two of these subs I would get a Rockford Fosgate Punch 301M which would give your subs 150 watts each in 2 ohms. If you have any questions about how to wire your subs or anything like that lemme know.
Also JL audio and Boston acouistcs do not allow anyone to sell their products online. If you do see a site that sells them and you buy them then you may be getting a bad product and you will not get a warranty from JL. AVOID ebay at all costs. same thing happens when you buy from there. Also buy some good wire for your amps and speakers from someone like Stinger or Streetwire.
http://www.jlaudio.com/subwoofers/10w3v2.html
http://www.jlaudio.com/subwoofers/10w0.html
http://www.jlaudio.com/evolution/tr.html
http://www.bostonacoustics.com/ca_product.asp?Productid=68&CategoryID=14
http://www.bostonacoustics.com/ca_product.asp?Productid=233&CategoryID=14
http://www.bostonacoustics.com/ca_product.asp?Productid=86&CategoryID=14
http://www.crutchfield.com/cgi-bin/S-BFmUSmqmsug/ProdView.asp?s=0&c=3&g=110&I=575551S&o=m&a=1&cc=01&avf=Y
http://www.crutchfield.com/cgi-bin/S-BFmUSmqmsug/ProdView.asp?s=0&c=3&g=110&I=575301S&o=m&a=1&cc=01&avf=Y
http://www.crutchfield.com/cgi-bin/S-BFmUSmqmsug/ProdView.asp?s=0&c=3&g=130&I=575301M&o=m&a=1&cc=01&avf=Y
http://www.crutchfield.com/cgi-bin/S-BFmUSmqmsug/ProdView.asp?s=0&c=3&g=300&I=500CDM9823&o=m&a=1&cc=01&avf=Y
http://www.crutchfield.com/cgi-bin/S-BFmUSmqmsug/ProdView.asp?s=0&c=3&g=120&I=575301X&o=m&a=1&cc=01&avf=Y
http://www.crutchfield.com/cgi-bin/S-BFmUSmqmsug/ProdView.asp?s=0&c=3&g=120&I=500MRPF240&o=m&a=1&cc=01&avf=Y