[mikegett]

I agree with thesounddemon. There are no exact rules to what sounds good. Just what sounds good to you. HU's have come a long way. A few hundred dollars can get you a very nice HU. I suggest looking into what options you feel are best for you. The only must I would suggest, is ensuring that your HU has a subwoofer crossover. Most amps come with one built in, but not all. I realy suggest going to a nice shop to preview some subs. Avoid just going by your friends advice. While they all have distinct sounds, they are very prone to poor installation. The best sub underpowerd or in the wrong enclosure can easily dissapoint you. Once you figure out what type of sub you like, choose your amp. Try to avoid underpowering it. At the least match it to the RMS. At best, double it and lower your gain.