I've always had cars from the age I was allowed to drive, and each one I've always tuned and modified, one of the first points to get upgraded is the sound system.

I like having a good quality sound system but none of this heavy base that loosens all the trim on your car rubbish, just a good quality, capable sound system to give your music the best base to play from without going mad.

On my last car I ran a middle of the market Kenwood head unit with a 6 disk changer, in which I generally have a wide variety of music from pop to dance. I hunted around for a while looking for the right speakers to go with the head unit, so took a trip to the local car stores to have a play and listen to the speakers, and luckily they had my head unit on display so I was able to actually hear how the HU worked with each set of speakers.

After trying many kinds I decided on the JBL GTO6527S speakers at £60.00. The reason I chose these over others out there was just down to the sound quality and lack of distortion. With the base and treble up full and mid to set to 2 the speakers were excellent up to near on max volume, now obviously I knew that the tester boards don't represent how they will sound in a car, but they were the best I tested in my price and size limitations.

Once I got them home I set about installing them, and I have to be honest they were very easy and straight forward with excellent instructions for first timers wanting to do the job themselves.

Set the speakers and level up on the head unit and closed the doors and went for a drive with my favourite CD selected. To say I was impressed is an understatement; the sound quality was so good it felt like the bands were in the back seat playing directly to you. The sound just was so clear and vibrant that you felt the track instead of listening to it.

Overall, for the money the speakers are ideal for anyone looking to fill a 6.5" speaker hole. Obviously a decent head unit is a must to get the full potential of any speaker but these JBL speakers make even my inexpensive Kenwood head unit sound brilliant.

edit: forgot some of the specs for these speakers.
the GTO6527S's are 6" Coaxial speakers rated at 55W RMS with peak power rating of 165W - more pecs bellow

Power Handling, RMS 55 Watts
Power Handling, Peak 165 Watts
Frequency Response (±3dB) 55Hz -- 21kHz
Sensitivity 92dB
Mounting Depth 1-13/16" (47mm)
Cut-Out Diameter 5-11/16" (145mm)
Impedance 2 Ohms

(above spec list from JBL site)