Rumors as I've heard them says new cards won't be out until next year. Late spring or summer time, although Nvidia might release something sooner seeing as their cards aren't so hot right now. AMD's next cards are rumored to be not much better then their current cards. They are expected to be not much more then a die shrink, allowing for faster clocks.
In my opinion, seeing as the currents cards are pretty good, and the next gen is anyones guess for Nvidia or just a bit better for AMD, you might as well buy now. Wait for a good deal for the holiday sales and buy a current gen card. It won't cost much, and the next gen cards probably won't be much better. As a side note, Nvidia's next cards are rumored to be DX10.1, although we've heard this before.