You might try to buy a ATI HD4670, as its a VERY energy efficient card.
Ive got a Packard Bell PC here, with an athlon 64 x2 2.2ghz and a 4670 running stable on a 250W PSU, so that shouldnt be a problem. Also, your CPU is very energy efficient, so it should work. It can play most new games at mid/high settings.
You could also upgrade your PSU to 500W, and buy a ATI HD5770 or ATI HD5830
With out replacing the PSU your best options would be HD4670 or HD5570 which is newer and has even less power consumption, they are similar in performance. If you were happy with the 6200 card you are going to be even happier with the cards suggested.