PS note:
Phis idea about putting a fan in the PCI slots (free ones) I don't think is a good one. The reason is that your intake fan in located at the bottom, so if you put a an at the back-bottom of your case, it will take the air that your intake fan blows out, reducing a lot the airflow. Best setup is:
Air gets from the front and botom of the PC and flows to the back top of PC
Here is a little drawing for the airflow. Excuse the simpliness, but I did it in 5 minutes Too lazy to look for something better in the web Airflow