[ryanj247]

if xp:
pretty much any decent pci video card should do unless you're getting the 30" in which case get a card that supports dual-link dvi-d.

if vista (or if you're planning to upgrade to vista):
you're going to want to get a motherboard that has two pci-e slots, and get a 2nd pci-e video card with a chipset from the same manufacturer as your current video card. again, if you buy the 30", get a card that supports dual-link dvi-d. if you don't want to do all this, you can just install a regular pci video card on your current motherboard, but you will have to use XP drivers and won't get vista visual features such as "aero".