Budget being around $500-$700, already have a head unit.. Any suggestions?

yes... raise your budget

honestly man thats more then enough for a nice little system.. two alpine type rs and a ap1500 would do well.

depends on what you are looking for. between amazon.com and sonic electronix, you can put together a descent setup for that. i would recommend alpine aswell.

alpine spr-60 components- 150 sonic electronix ( little cheaper on amazon)
alpine swr-12d4- 150 ( little cheaper on amazon)
alpine mrv-500 - 133 on amazon( well run the sub comfortably, will get loud as you could want it without entering an spl competition and will not burn up your coil or overheat itself)
alpine mrv f300- 135 amazon (will underpower the components unless you are only running a front stage, then you can bridge it. but dont be fooled, even at 50rms, you will get great sound from these speakers. night and day from factory. nice and loud with no distortion at high volumes.
if you need or desire a rear channel

alpine spr-69c-100 on amazon

it will be a complete system in the ballpark and get loud and stay clean.

if you want it will within your budget, go witht he type s of each of these.. it is a step down but the sub is 500rms and it based on the old type r which people raved about. will still sound great from entry level audio. some dont notice the difference in fidelity aside from the fact that the r's produce phenomenal midbass/range. same amps.