AMD HD3870 X2 Crossfire
 

A little over three weeks back, AMD unleashed their HD3870 X2
graphics card which put AMD back on top for the fastest graphics card.
Although the card featured a Crossfire connector bridge, drivers were
not available to take advantage of this feature. AMD has now released
their 8.3 Catalyst drivers that allow you to run two HD3870 X2
graphics cards in Crossfire mode allowing you to harness the power of
four GPUs.

http://www.tbreak.com/reviews/article.php?id=589