Duel video cards VS Correct MB with video card

I do appreciate all the replies I have gotten, as before some of you have suggested a motherboard and adding a video card with duel outputs to support three monitors. Some have suggested that by installing the new video card by default it will disable the onboard video leaving me with two working outputs and still no three monitor s working. I am an enthusiast, and by no means an expert, but do have a basic understanding of this stuff (probably just enough to get me in trouble).So the question still remains what is the best way to go? How do I know if a motherboard will let me install a video card and have all three monitors working? Is a motherboard with no onboard video, the best way to go and install two identical video cards with duel outputs? Any additional help would be greatly appreciated as I am going to order a machine this coming week, and would like to be as informed as possible as to the best configuration.

A very confused but optimistic enthusiast!