For net buys, I've used Crutchfield a lot www.crutchfield.com
The prices are good, but even better the service is awesome. And when you buy speakers and stuff, you get free detailed install instructions and connections (saves and extra few bucks). You might get better prices elsewhere, but not by much. Also try www.thezeb.com
Prices are good and service is average, but I've had no problems with them.
Yeah, the stock Infinity speakers were crappy. When I took them out, the foam surrounds pretty much disintegrated on the spot. "Real" Infinity's are SO much better...