how big of a power supply do i need?

for 2 8800gtx'sl1mIt

id go with a 750Watt to be on the safe side but thats just me. 

Most brand name PSUs with around 45+ amps on the 12v should be fine for 8800GTX SLI. The Corsair HX620 is one of the best PSUs around at the moment. Silverstone Zeus series PSUs are also great quality. 

http://www.legitreviews.com/article/462/1/

This is the P.S.U. that I want.

roulettethedog

That's funny, that's the PSU I have ;)

The trick is quality over quantity for the most part (and yes, brand names USUALLY mean quality.....they are a known brand for a reason). The Corsair 620 has a great reputation and handles things that, by all estimations (like that calculator) it shouldn't be able to. According to a similar calculator I used before, a single GTX with an OCed Q6600 required an 800W+ PSU. The article roulette linked has the 620 running SLI GTXs with an OCed QX6700.

and they're supposed to be quiet..

http://www.silentpcreview.com/article692-page1.html