This structure just above is the classic answer given when students are asked to draw the Lewis dot-diagram for CO2. However, there is an interesting resonance that is not discussed in the main resonance page. In these two forms, the pi bonds are at 90° to each other. Let us say that one structure has the left-hand pi bond in the xy plane. The the right-hand pi would be in the xz plane. The second resonance structure would reverse the orientation of the two pi bonds.
Here are the other two resonance structures:
Pauling identifies the percentage contribution of each structure to the actual "resonance hybrid" as 25% each.