What is your budget for this? Do you want something that is going to just drop in or are you looking to put a little more work into it for something custom? You are also going to need at least one amplifier for the subwoofer, and another one for the front stage would be best.
Subwoofers, what are your goals? Do you want something that is just flat out loud, quality, what? *Don't say, sound flat out loud, and high quality. Doesn't exist*
Here are some quality subwoofer manufactures
Sound Solutions Audio (SSA)
Mach 5 Audio