i'm going to agree here, and add a little.

Kicker, JL, alpine, (insert name here) they all make good product, but product is not the answer, a good installation is.

#1, your getting a LOT of different opinions on specific speakers, and to each of them they all probably sound just great, these days you can get some nice quality stuff pretty dam reasonable and do with one 12 now that took 2 12's not so long ago.

a good quality 10" or 12" will work fine, and 400-500 watts is fine, spend a few bucks more and get Dual Voice Coil, but if you don't that's ok too.

The BOX is the key, you can have a great speaker setup and a great amp, but if the box isn't right, your system might as well come from walmart. If your not into the DIY or are not experienced in the audio end, find an installer first, show them and tell them what you want, keep your spare tire in mind and if your guy has some woodworking skillz to go with audio experience, you can build a nice amp rack, place the proper box correctly, have a good looking and good sounding system with about 40 different setups, but if you're not placing the proper box correctly, your fugged.

for me, on the system i'm building now, alpine HU, alpine 400 amp, single JL Audio W6 DVC 10", I also have a 12" w3 JL audio but i'm leaning against it due to trunk/spare limitations so I picked up a 10" instead.

I repeat, a Quality single sub, 10" or 12" with a quality 400-500 mono amp will be Just Fine !!! you don't need to overpower it, just run DVC with 2 or 3 ohm, and imo a cap is for a performance user, skip it and spend the extra few bucks on a sub thats a step up, These days, quality = quantity and for a couple hondo, you can pick up some nice stuff on Craigslist too, don't eliminate that from your search.

in the end, all of our opinions are just fine and dandy, might give you some nice google links, and help you speak intelligently about your needs to the installer, but your installer (and maybe a 2nd opinion) is the key, cuz he is the one that should be building your box, and if he builds the right box for the right single sub, puts it in the right spot you'll be loving your low's, and still have 75% of your trunk. if your installer is sub par, you'll still like your low's but you won't know what your missing.

there is nothing better than a back massaging thump when you want it, but make sure is a thump, not a rattle, and to make sure of that, the key is the installer/box. your just the parts collector. If you don't know what your doing, you buy the right stuff but put it together wrong and you won't get what your looking for. Even if it "sounds good" it will never sound "great !" until you get a good install.