Ok, what you want is any "SLI" ready or "CROSSFIRE" ready power supply. See this:
http://www.tomshardware.com/reviews/radeon-hd-4890,2262-13.html
Note that this card pulls a LOT of working watts. 285 working watts to be exact.
Let me explain there are two kinds of watts, one is RATED watts and the other is WORKING watts. The RATED watts are the watts that are rated on the power supply. So if you buy a 650 Watt PSU, this is its RATED wattage. However, no power supply is 100% efficient. There is always a loss of power from the AC to the DC side of the power supply. The best quality psu's have an average WORKING wattage of 80% of the RATED value. So an 80% efficient 650 watt PSU is = 0.8 X 650 = 520 WORKING WATTS. Cheap power supplies can fall significantly in their efficiency due to lower quality components...as low as 50%.So a cheap supply might only give you 0.5 X 650 = 325 working watts! I know, pretty lousy.
What this translates to is lost energy which you are paying for on your electric bill. It also translates to a hotter power supply because lost energy, instead of being translated into physical electrical work is instead translated into heat. Heat degrades electrical components and shortens their shelf life which means that you have a cheap power supply made of cheap components that burns out rapidly or fails rapidly. Thus, buying a cheap power supply is NEVER a smart idea. Neither is running a power supply on the bleeding edge of failure, which helps to burn out power supplies as well.
Now, what you want to have is a good quality (and thus, more expensive) power supply, rated at 80% efficiency or better and that provides a general formula like this:
Total Needed Watts for everything else on the computer + Total MAXIMUM Watts for the video card + about 25% more as a buffer (for expansion).
SLI or CROSSFIRED cards like this one pull an enormous amount of power, produce a lot of heat (nVidia cards even evolve more heat than ATI cards due, due to GPU architecture). I would say that the average computer, all components thrown in, need to have an average of about 300 watts of working power. Throw this ATI card in, and you have another 285 working watts
300 + 285 = 585 Working Watts
585 x 0.25 = 146 watts for expansion
Rated watts = (585 + 146)/0.8 = 914 Working Watts.
You can lower the extra percentage if you want, down to 850 watts just to be conservative. An 850 Watt rated supply gives you a working wattage of = 850 X 0.8 = 680 working watts. Remember, we calculated you needed a minimum of 585 and an 850 watt psu at 80% efficiency gives you 680 so you have more than enough watts, by about 70 working watts.
This means you should be looking at 850 Watt power supplies with an 80% efficiency rating. You should stick with ANTEC or CORSAIR, which I consider the most reliable. You can now go out on the net, to Newegg or Tiger Direct or any number of places an investigate SLI or CROSSFIRE ready 850 Watt PSU's for yourself.