You can also put in an additional 120mm fan in the middle of the case. It would blow air from either the top or bottom of the front fans throught the case, depending on where you put it.
But it does make the drive bays where you put the extra fan unusable.
You can see the detachable enclosure for the fan in this
picture. It is the black thing near the middle of the case.
You can also see it a little more clearly in the picture two spots to the right of the one I linked to.
I own this case, so you can trust me on this.