Intel X58 chipset has 36 PCI Express x1 lanes (just for comparation, AMD 890FX used on Crosshair IV Formula has 42 lanes) and on Rampage III Extreme ASUS arranged these lanes on four PCI Express x16 slots.
The first PCI Express x16 slot works at x16 if the second slot is empty. If there is a video card on the second slot, both the first and the second slot will work at x8. The third and fourth PCI Express x16 slots work the same way: the third one works at x16 or x8, depending whether the fourth slot is empty or not. So if you have two video cards it is really important to use the first and the third (and not the second) PCI Express x16 slots in order to get the best performance possible. Using the manufacturer nomenclature, this motherboard supports the following configurations: x16; x16/x16; x16/x8/x8 or x8/x8/x8/x8. The slots are compatible with SLI and CrossFireX arrays.
The motherboard also comes with one PCI Express x4 slot and one standard PCI slots.
Keep in mind that the absence of PCI Express x1 slots is not a problem, because PCI Express x1 expansion cards can be installed on any type of PCI Express slot (x16, x8, x4 and x1).
The fourth PCI Express x16 slot is located at the edge of the motherboard, so if you install a two-slot video card you will need a case with eight or more expansion slots.
Near the first and the fourth PCI Express x16 slot you can see two standard peripheral power connectors, which can be used to help to power high-consumption PCI Express cards.