AnandTech: NVIDIA's GeForce 6 SLI: Demolishing Performance Barriers. The coolest thing out there. You can now slam two video cards into a single machine. The first board out is the ASUS A8N-SLI Deluxe (nForce4 SLI) Motherboard. Available for about $180. Its a dream motherboard if you want SLI, otherwise get the nForce3 and a AGP card and you'll be in good shape. Here's their net that adding as second graphics card increase performance by about 70% over a single one. That's pretty amazing scalability.
bq. if you've only got $400 to spend on a card today you can't beat the 6800GT as a single card solution. Then, as the price of the 6800GT drops, it may become more attractive for you to upgrade to a second card rather than buying a next generation GPU. As long as we’re between DirectX cycles, SLI enables you to have the fastest most robust graphics setup out there without missing out on much.
You should be able to get the ASUS board and a "Gigabyte":http://anandtech.com/mb/showdoc.aspx?i=2285 board before Christmas. Drool ho!