yes two 8800gts's will require more power then one so for sli you are probably looking at a good 600watt one (or higher if you can afford it). Brands that work are corsair, pc power and cooling, seasonic, enermax ... Probably one of the best psu's out now in terms of budget/wattage for a power user system (but not an insane one) is pc power and coolings silencer 750, its not cheap but its very good quality and quiter then most of their psu's. Also keep in mind that as long as you go with a good brand it cant hurt to buy more then you need and in fact may save money in the long run (better psu's are more efficient which means lower electric bills).