I would kill (a software bug) for a GTX295.
They are a little more expensive then the 4870X2, but generally better. I am still waiting for them to go in stock in my country, even if they cost a lot more then in other parts of the world (US gets the best deals IMO).
However I wouldn't bother with a Quad GPU setup (dual 295), it doesn't show good scaling yet, and when it will, it will be to late, GTX300 will most likely smash the 295.
I have a 30" Dell and so far my 8800GTS 512MB worked great, but I kinda feel the need for speed by now.
A 4870X2 would serve anyone just as well, but I don't yet trust ATI with their dodgy drivers yet. And nVidia surprised me in a good way with the 180 series.