That PSU is overrated. You could probably safely run a 4670 on it. A budget of up to $150 will allow you to replace the PSU (e.g. with an Antec Earthwatts 430) and still get a 4850, but if you'd rather keep it to $100 or less, go with the 4670.
those are to be on the safe side. if your feeling lucky you can try a 4830, 4850, or 4770. whatever you feel like spending, you cant go wrong with either. i think a gts 250 or 9800GT might be pushing it with 19A and a cooler master brand.
if it were me i would get this 4850, for $100 its a steal
id go with the new 4770, since it runs on 40nm (as opposed to 65nm in every other card availible today), it is cool, quiet, and less power consuming. dont try to get the very most power consuming card your psu can handle, because, depending on your cpu, it may not be enough to hold up your whole system.
BUT wait until next month, ati is supposed to be releasing their new rv800 gpu, which will all be 40nm, more stream processors (good), and it will run ms new directx 11. also it will generally be faster. i was gonna buy a 4870x2 but decided to wait until the new series comes out.
EDIT: sorry current cards run 55nm, some older ones like the gtx 260 runs 65