ATI has now officially announced their new CrossFire technology which will enable users to install 2 graphics cards in their PCI-Express PC.
There are previews around already, probably the most interesting is the one over at
Anandtech where they've managed to somehow get a chart showing the relative performance of CrossFire compared to a single card setup when running Doom3, and some photos of the Catalyst Control Center CrossFire panels.
Here's a list of some of the others:
ATI also has a new section opened up on their website dedicated to CrossFire, you can check that out
here.