Yup, Nvidia cards have a feature in the drivers that let you turn the screen 90 degrees. The cheapest
decent card would be a
Geforce 6600GT and I know some of them have dual DVI. The newer more expensive models like the
7800 are even easier to find with dual DVI.
The only thing I can think of that might not be so good is that Cleartype probably works better with the monitor in landscape mode.
I think Bill Hill mentioned something about that in his latest C9 video.