The gtx 560ti would be the way to go, unless it's outside you're budget, then the Radeon HD 6870 would be the next best thing. If you're able to spend a little more money you may want to check out the Radeon 6950 2gb (If you can find one) or the Radeon HD 7850.
I can't tell what my power supply is rated at without taking it out of the case. I realize I need at least a 500 watt one and will replace it if it is lower. Judging from the forum here the corsair supplies would be the ones to go with.