"Support for PCI Express x16 graphics cards up to 150 watts and with up to 512MB graphics memory including:
NVIDIA Quadro® FX 4500; NVIDI, Quadro FX 3500; NVIDIA Quadro FX 3450; ATI™ IreGL™ 7200; NVIDIA Quadro FX550; ATI FireGL V3400; NVIDIA Quadro NVS 285. All graphics cards support dual monitor configurations"
So i guess it just depends on how much money your willing to spend on a workstation graphics card.
i think the FX550 is prob. the best. But I don't know that much about Quadro