I am looking for a motherboard that I can use two PCI -Express video cards in to connect 4 monitors.
Not sure if this is possible or not.
I've seen a lot of boards with two PCI-Express slots but most say you need to use SLi or Crossfire and it only allows one or two monitors.
No, you want one of those SLI/CF motherboards. Put your two video cards in, and don't enable SLI/CF. Depending on the board, the second slot might be limited to PCIe 1X bandwith, but newer boards should provide a full 16x. Pick a board you like, then read the manual, it should say something about this.