Going further down the scale i have seen benchmarks that show a pair of 8800GT cards are a match for any single card at the moment.
if i was to go with the 9800 gtx+, i would have to go with the SSC edition. h 2 9800 gtx+ ssc or 2 gtx 260
Seconded on the SLI 260's, newer tech and better scaling for around the price of a single 280.
what would be the best 260 to get?
Probably a basic EVGA one, they are the cheapest card for the best support and can be OC'ed very easily.
Also EVGA is not on nVidia's chopping block so you will continue to receive support, EVGA's RMA process is pretty good if you have a problem and there is always the step-up program if something better and cheaper comes out in the next 90 days.