I think the best would be a Nvidia 440 GT. It recommends a PSU of only 300W and uses no power connector. However, a 240 GT looks to have the same performance and requirements.... I would get whatever is cheaper.
However, If you want to play games I would look for something with a power cable. Graphics power increases a lot for cards that require power connections.
Thanx. But I am planning to buy nvidia xfx 9500gt. I am using a 450 watt smps, gigabyte g41 chipset with 2gb ddr2 800 ram and pentium dualcore 5400 (overclocked to 3.1ghz). Now, suggest me... Plzzzzzzz