All Geforce4 TI/MX and Quadro4 based cards support Twinview (sometimes called nView now). Other cards that support Twinview are Geforce2 MX and some Quadro2 MXR cards.
I won't go for GF2 MX / Quadro2 MXR based cards since those cards aren't that great. The OpenGL performance is not that great but that is not the biggest disadvantage. Those cards are using nvidia's first generation of Twinview. The first Twinview version didn't support high resolutions and refresh rates on the second head.
On Linux Xinerama (read multiscreen) works great using one Nvidia card. OpenGL works on both heads. When you use multiple Nvidia cards in Xinerama mode only one will have OpenGL. (very buggy using multiple cards)
If you will use the card in a business environment where money isn't that important I wouldn't choose a Geforce based card but a Quadro based card instead. (Quadro is the professional Geforce)The cards and GPU's are the same but on Quadro based cards you have some extra features in the drivers that might be usefull and the drivers are more tweaked for non-gaming apps. The only manufacturer of those cards is PNY: http://www.pny.com/quadro/
All cards except for the GF2 MX are an option for you. The choice depends on what you really need (performance wise) Only make sure the cards are shipped with 2 outputs (or 4 outputs for the Quadro 4 NVS 400).