Every modern day video card can output to two monitors, AMD Eyefinity cards even up to 6 monitors and the nVidia GTX 680 up to 4 monitors.
So if you only use a single monitor and want to add a second monitor, you probably only need the correct cable. If you use dual monitors and want to add a third monitor, then your choices are limited to the 680 or an AMD, or two GTX 4xx or two GTX 5xx cards that use the same driver.
I want to look more into this solution, because I might get into trouble using a black magic intensity pro with a newer asus motherboard (the line of recommended boards is very narrow).
I have the GTX 570 installed in my PC and would install another GTX 4/5xx card too - so far so good :)
How would I get the timeline output on one of the outputs of this extra card? Should I put in a setting in PPRO?