How much power do i need in an amp? New Subwoofers and Car stereo for Xmas?

[Epik Username]

I'm getting a new car stereo for Christmas and either 2 subwoofers or a couple new speakers. If i did get 2 of these subs, this one for example: http://www.bestbuy.com/site/Kenwood+-+12%22+4-Ohm+Single-Voice-Coil+Subwoofer/9231574.p?skuId=9231574&id=1218063832074 , paired with this stereo: http://www.bestbuy.com/site/Sony+-+52W+x+4+In-Dash+CD+Deck+with+MP3+Playback+and+Detachable+Faceplate/1149978.p?id=1218225364694&skuId=1149978&st=car%20stereo&cp=1&lp=8
What kind of amp would i need?