Until recently, I was running a triple head monitor set-up off of a Matrox Parhelia (tri monitor video card). FWIW, I was running CRT monitors off of this set-up. Now, I just use the card in dual-head mode and I am able to set the res to 1600x1200 to increase the screen real estate. With the Parhelia set to its defaul it sets to 3860 x 1024 or basically 1280x1024 across three displays... The costs of this card have decreased since I purchased it last September. I think it got some mixed reviews from the gaming community, but I think its a good solution for trading.
I have a Geforce 4 4600 in my AGP, and I added 3 Matrox G450s (PCI). Works great. Every card I have can output to two monitors.