if you get an asus motherboard with pci express slots they can take up to 3 graphics card on certain mothorbpoards, with each card being compatable to run 2 moniters, so you could have 6 displays running if you wanted to. im curantly using an nvidia geforce inno 3d 8800gt and the flight sims are breath taking.

Also forgot to mention with nvidia graphics cards you can stretch your display accross as many moniters you have connnected to your computer. you can find these setings in the nvidia control pannel hope this info helps you.