You can pick up good GPUs at newegg.com. However, due to the low wattage of your Power Supply Unit, be sure to check the recommended power supply minimum wattage for the card you're looking at.
This card -might- work: http://www.newegg.com/Product/Product.aspx?Item=N82E16814161374
But if you're not gaming or anything, try going for an AMD HD6450.
No matter what card you choose, throw your system info into this Power Supply Calculator just to see if it will work with your 250 watts.