Ok, and welcome to car audio. Ignore those who are pressing you for pictures.
Im going to give you a very quick lesson on the simple stuff for car audio, starting with the basics.
Subwoofers come in many beautiful shapes and sizes! Some are 8, some are 18. Some are red... just not the good ones. Depending on what you want, you need to determine size. The lower, the quieter in general. The bigger, the louder and deeper. 12s are probably most common, because they are good for the price, provide relatively good lows, and good volume. Certain 10s (polk momos in a certain style box) produce good loud bass too, just not as often. See if you want low, hard hitting, loud, or more accurate bass. Either try to figure out or just post here and we can try to figure it out. I would say for your purposes, be looking at either two 12s, two 15s, or a single very good 15. Whatever sub you look at, look for the RMS rating... everything else is basically just matching an amp. RMS.
RMS is simply continuous power. If anyone ever says "peak power," slap them and walk away offended, because they just said "hey i think your a dumbass and I want a bonus on my next paycheck so im gonna sell you crap!"
Amps... im not going to say much about ohms and that crap, but you will have to worry about that later. First decide what sub you want, then ask here or somewhere else how to match an amp. All you really need to do is look again for RMS. If you have a single 400 RMS subwoofer, you need a 400 RMS amp. Dont really worry about that stuff right now, ohms and all that stuff is complicated, and unless you actually have any desire to really learn everything, you wont need to know that.
Wiring is simple, but depending on the amount of power, you will need to adjust gauges. Grounding cables, look at around 4 gauge, speaker cable around 8-12gauge. 10 is usually spot on for ample power without too big of a cable. Just remember, the smaller the number, the bigger the wire when it comes to gauge.
As far as brand names, Dual isnt even there. Sony xplod is the worst crap out there. Dual is also right there with them. For reference, I have a single 15" subwoofer with 600RMS, and this is all very nice name brand stuff for 400$ total (amp and sub) plus another 150$ in box and wiring and its very loud.
For cheap, high quality stuff, I would look at certain off-brands. Massive Audio is my sub, they make very good relatively cheap subs. Fi is getting big, but look at them. Some used stuff may be cheaper. Otherwise, Alpine makes some great stuff. Kenwood I usually wouldnt consider, but they now have some new subs out that are decent. Pioneer makes some cheap but good subs. Just do your research, before you buy anything, check reviews on epinions.com,
amazon.com,
crutchfield.com, and wherever else you can. Read what people like, dislike, etc... if the particular sub your looking for is GREAT at something you dont want as much, consider maybe not to go that way. If it sucks at something you may desire, definitely ignore it. Reviews are very important, and you can get good cheap equipment that works well by simply checking around some sites to see what people are saying.
I remember you mentioning you did want it loud. If so, dont get a single voice coil (SVC) sub. Get a dual voice coil (DVC). Slightly more expensive, but infinitely better quality and loudness. What it all comes down to too though is your box. We will certainly help you with dimensions and stuff, but consider just buying a premade one.
I think I covered just about everything... if I left anything out, feel free to chime in anyone. If anything is wrong, feel free to pretend I care //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif.
Hopefully your still not as confused as to what everything is. Certainly thats not light reading or what you probably wanted, but just basically ask us if you have any questions.