i got 2 12 inch kicker comp VRs and a kenwood 600 watt max amp. it knocks pretty hard and the set up wasnt that much money. 100 for each sub, and the amp was like 200 bucks at best buy. the box was free and the wiring was a bit expensive.
i agree that that is way to broad of a question i know someone that has some cheap kenwood 12s and a 100 watt amp that he listens to and then theres me who has some MA Audio 12s and an 1800 watt amp so mean it all depends on what you want to spend as to how far your system goes