What is a good Video Card to pair with i5 3570k?

I just bought a i5 3570k as part of a full computer upgrade. I'm having trouble knowing which single GPU would be good to pair with it. I need something that puts out some might power but also doesn't take up a lot of wattage as i'm only on a 400 watt psu and am not looking to upgrade that. I tend to lean towards nvidia cards but I'm willing to give AMD a shot if I have to. The card I've considered the most is a EVGA GTX 660. If anyone has some tips let me know.

Some of the 7870s are on sale or you could get a 660ti.

Get a 7870! You can overclock it to near 7950 performance. And it's a bit cheaper than the GTX 660 right now.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814102983

Sorry forgot to mention my power supply only has one pcie connection so a 7870 is out of the question. 

http://www.newegg.com/Product/Product.aspx?Item=N82E16812887001

I know you can use a molex adapter but I don't really trust putting a high price card on an adapter. 

What kind of games are you going to play though?

BF3, COD, torchlight 2 and the crysis games.