It really depends on your budget. This is the sort of system i have planned for my next car:
-Headunit (already have this:alpine 9807, $499)
-Hertz Energy 165mm 2 Way Splits $199 at
http://www.webaudiodirect.com/-some kind of rear fill (already have these, pioneer 150w 6.5in,$100 + $20 for caps to high pass them)
-1 subwoofer (haven't decided what yet, $150-200ish)
- jaycar 4x100 amp, 2 channels bridged to give 300wrms to the sub, the other 2 100wrms running the splits, $350)
-sound deadening, cables, sub box, roughly $90
if you can give a ballpark figure as to what your willing to spend, then it'll be easier for me to give you some specific advice.
Running 2 subs will make it considerably more expensive because you'll have to get an amp for the splits as well. eg 4x100 bridged to give 300wrms each to the subs, then a 2x84 for the splits. (so you'll need to spend $200ish for another sub, $180 for another amp, few bucks for some cable for the amp)
Last thing, if your going to run two subs, and you want any decent SQ, you'll NEED an amp for the splits. Those subs will drown out any mids and highs if they're ran purely off the HU. If you're only running one sub, the splits will do OK off the HU, but sooner or later you'd probably want to amp them when the car audio bug sets in
anything else just ask