Quote from Scataphagos:
1st. Your mobo should have at least 2, PCIEx16 slots. That will let you run 2, dualheads = 4 monitors.
I've used ATI, Matrox, and Nvidia NVS in multi-card rigs. Currently using Nvidia Quadro NVS 295s. Other guys like GeForce 8400GS or equivalent ATI cards. Fanless is better... less noise from your box.
If you're going to game as well with this computer, you'll probably want more horsepower in the video card. If it's strictly/mostly for trading, general computing, watching movies.. than the 295 or 8400GS will be just fine.
And correctamundo about tech guys not being up to speed with their multi-card knowledge.