From the THG Article AMD's New 780G Chipset
In that article they used the motherboard graphics for 2 monitor and an ATI HD 3450 video card for the other two monitors for a low cost solution to run 4 monitors.
Besides the option in the article above you have quite a few options actually. Most video cards can run two monitors. And most motherboards can have two video cards - usually 1 PCI-E PowerColor HD2600Pro PCI-e $48
and 1 PCI Powercolor HD2400Pro PCI $45
The slightly more expensive Crossfire or SLI motherboards can handle two standard PCI-e video cards.
Having a display spread across two monitors is usually called Span mode
(also called stretched mode).