ASUS N6800GT SLi -
The ASUS card currently retails for $489 at newegg and multipling that by two for an SLI setup gives a figure with which you can easily buy an entire PC with reasonable performance. They also says: "We think that playing with the 6800 series in an SLI mode is only for the rich kid's at the moment. As prices come down and more games take better advantage, only then will we be able to recommed an SLI setup."