I'm currently using a NIVIDIA GT 240 video card. It has three outputs but will only allow me to use two monitors at a time.
What model video card gives good support for three (3) monitors with FSX? I'm on Windows 7 with 16GB of Ram, etc. and have a 750w. Power Supply.
Like RM said, triplehead2go is an option though depending on the monitors those resolutions can get pretty huge for a graphics card to support. You might look into an ATI EyeFinity setup-
I'm currently running 3 23" monitors from a single ATI HD5850 graphics card. There is a bit of a caveat, however. For EyeFinity to work, one of the displays must be through the DisplayPort output on the card. To achieve this, I am using a passive DisplayPort to DVI adapter, which is ideal for displays under 2560x1440 maximum resolution. For the higher resolution dislays, you need an active DP to DVI adapter.
So assuming that you have three displays capable of taking a DVI input and they aren't 30" screens, I would suggest an ATI card and a DisplayPort adapter.