Don't waste your money on headrest TV's, thats just for show and you wont get to enjoy it to its full potential. Start off with a head unit/subs/amp. If your planning on spending upwards of 1500 on your setup you could do an in dash touch screen HU for like 400-700 depending on the quality you buy. Thats if you really want a some sort of display, although I would rather just spend the money on better subs/amp.
As far as what type of subs and amp to get, I will probably get a lot of hate for saying this, but if you want something better than what your friends have, avoid all the common name brands like pioneer, clarion, alpine etc.
Most of the shops around you will probably swear buy it and charge you an insane amount for low-mid quality products when there is better options out there.
A few good companies to look into sub wise would be
Fi Audio
Stereo Integrity
SoundSplinter
All three offer high-end subs in the same price range as the alpine/pioneer lines but give better performance.
As far as the amp goes to power them, look into
Sundown or
US Amps or even
Rockford
You could ignore all that and go with the JL amp/sub combo but for the most part your just paying for the name, although they do make very high quality products.
As far as HU's go, do some research and read some reviews on whatever has all the features your interested in (iPod ready). Eclipse, Pioneer, Alpine make some pretty solid head units, but like I said their subs/amps lack in some areas.
Remember, you may find the subs and amp to fit your price range, but unless you know how to install the equipment yourself, plan on paying top dollar to have it installed at a shop or look around and find someone local to do it for less. You will also need to set aside money for a sub box and all the needed wiring.
I just went through all of this the hard way so I hope it helps you out some in avoiding making the mistakes I did. I ended up going with
Alpine IVA-D100 (touch screen display)
2 Fi Q12's (rated at 1000 rms, although people put more than that)
Sundown SAZ-1500D (1500 @ 1ohm or 2000 @ .5ohm)
MB Quart PC216 Components
Sundown SAX100.2
Big 3 Upgrade (Electrical System)
I couldn't be happier with the setup, the Q's hit HARD and still maintain good SQ. It's also fun when your friends ask you if you got your subs at Walmart because they have never heard of anything outside of what the local shop will sell, and then they listen to them and retract their statement. Anyways, hope all this helps and I realize for the most parts its opinionated but everyone I've talked to that has gone this route hasn't had any complaints.
