I have a pair of Diamond speakers mounted in stock e36 housings. These are a pretty good improvement over stock speakers.
You don't need to run them from an aftermarket amp, but it always helps.
Here are the specs, and pics will be up soon:
6" 2-Way Speakers
Peak Power Handling: 120 Watts
RMS Power Handling: 60 Watts
4 Ohm Impedance
Textured Copolymer Cones
Butyl Rubber Surrounds
Heavy Gauge Proprietary Frames
Flat Progressive Spider
Extended Pole Motor Design
Rubber Magnet Protector
Aluminum Dome Tweeters with Ferro-Fluid Cooling
Integrated Crossovers
Bi-Amp Capable
Shallow Mount
$100