I was doing some research, and I came across this info from another site:
9600gt - minimum suggested
9800gt - good price/ performance
gts250 - solid pick for somewhat better performance but only if cost over above is marginal
gtx260/275 - money is no object
gtx285 - only if you find a ridiculously good deal
so anything in terms of most "cost-effective" would be in the 9600gt-9800gt-gts250 category. so look for the best deal you can find. ebay works.
I tend to agree with this post. What do you guys think? Agree? Disagree?