AMD 890GX chipset has one PCI Express 2.0 x16 lane that can be split-up into two x8 lanes if necessary. Translation: motherboards based on this chipset can have one or two x16 PCI Express slots, but they will work at x8 if two video cards are installed. The north bridge chip supports a total of six PCI Express x1 lanes, while the south bridge chip supports two more.
ASRock 890GX Extreme3 comes with three PCI Express x16 slots. The first two (blue ones) work at x8 if both are used at the same time, while the third slot (white one) always work at x4 (using four x1 lanes from the north bridge chip). All slots support CrossFireX mode, as expected.
The motherboard also comes with one x1 PCI Express slot and three standard PCI slots.