saveup for 6 months and wait for the next generation video cards, the current 9000 series cards for the price are not going to be a huge omg improvement over your 8000 series cards.
right now frys has the pny nvidia 9800gtx oc's for about 220 a pop. so you can find those cards for about 200 elsewhere. ok so 400ish for a marginal upgrade. (if you bought right now)
the gtx 260's are goin to cost more money for an upgrade, even in 6 months for a quad sli solution like that, at least 300 bucks a piece and by then 2nd grade quality hd cards.
I'd say wait for 10k series cards and stay with the gtx bracket in the same 500-600 price range. either way you got 6 months to save up, you'll find a good solution.