I've tried JL Audio, Oz Audio, Cerwin Vega, Sentrek, Realistic (lol), and Kicker.
JL is the best I've heard.
And like SilverDB8 said, the amp is just as important as the sub, and stay the hell away from Sony. A properly sized and properly built enclosure is important too.
Back in 1993-94 when I was buying cassette decks, Kenwood was my choice, they looked good and worked fine for me. I bought a couple of their amps in the early/mid 90's too....they were OK, for the money. I wouldn't bother with any Kenwood speakers.
Alpine has always been the undisputed king of CD players!
I know alot about this stuff, and if you want recommended subs, try www.soundsplinter.com, at first, there prices look high, but you realize they're not so high when you hear them. They're virtually distortion free. If your looking for something that is just as good as any mainstream brands, however half the price for what you get, then they're great speakers. Another good company is Ascendantaudio.com, they're a little cheaper and are on par with the soundsplinters as far as SQ and SPL, however, some say they don't look as good (but truely, sound isn't meant for looking at), and their customer support really sucks. However soundsplinters customer support is awesome. If you just want the average "kid on the block" sound, go with a 8 or 10.