This depends on the card being used and how many outputs are required. The Quadro FX 1800, Quadro FX 3800 and Quadro FX 4800 offer dual DisplayPort connectors along with a single Dual-Link DVI connector. The Quadro FX 4800 for Mac offers two Dual-Link DVI connectors along with a single Stereo connector.
It is important to note that for the Quadro FX 1800 and above, any combination of DisplayPort and DVI connected monitors can be used; however, only two outputs can be active at any one time.