Welcome to the forum.
The GeForce 560 1GB at $199.99(shipping included) "here"
fits the bill, if you have a PCI-e slot on that motherboard.
That card has a 3 year limited warranty.
This is the nVNews review of an overclocked 560 at: http://www.nvnews.net/vbulletin/showthread.php?t=159295
It's stickied at the top of this forum.
A similar product from ATI is the Radeon HD 6950 1GB. It costs a bit more at $209.99 with MIR "here"
and offers a bit more performance.
Here is a comparative review of those 2 cards at Guru3d.
You can't go wrong with either of those cards, but I personally still prefer nVidias driver interface. The ATI drivers are a lot better than they used to be though.