I have an Asus a8n sli board (with nforce4 chipset) and I'm very pleased (as with all asus boards in history
Everything is supported out of the box (onboard sound, pci express, sata drives, amd cool'n'quiet).
Especially that amd cool'n'quiet thing is really nice, if my computer doesn't have 100% cpu usage, the cpu wattage is halved. (Get an silent graphics card and you'll have an economic and silent computer)
You don't need to install the nvidia binary drivers if you don't want to. You cannot use accelerated 3D then. But if you don't play games or use open gl screen savers that would be no problem.
SLI doesn't work in Linux at the moment, you can however buy two cards, connect a screen to each of them and expand your desktop to two screens.