Some things to consider:
1. I am by no means an expert, and I haven't purchased car stereo stuff in like five years.
2. I'm biased towards JL audio and Boston Acoustics, which you might not want to spend the dough for.
3.You're after-market receiver will allow you much greater flexibility in choosing speakers. The higher output will allow a greater range of sensitivity levels.
4. You generally get what you pay for when shopping for car audio equipment.
I generally listen to a wide range of music, but moreso punk, indie, rock stuff....so you and I would generally prefer a 'tighter' bass so to speak. Round speakers (5.5", 6.5") are usually easier to get tight bass from as opposed to 6"x9"'s, or any oval cone speakers. Round speakers tend to last longer too.
Polk and Infinity have always made some quality low/mid end speakers (around $55-85.00), but there are several high end companies that make speakers intended to directly compete with them, for only a few bucks more.
Crutchfield happens to be located in my town, but they also have a very good online store, complete with some decent tutorials (under the 'learn' section). These can be very helpful, along with the easy matching they provide to your car's year, make, and model.
http://www.crutchfield.com