Enough to have an effective intake and exhaust system running through your case. It varies really. I'd reccomend atleast two. Four (not including heatsink, video card etc.) at the most since your not overclocking...
Ok thanks. I have an extra 80 mm fan lying around, so I'll use that as intake in addition to the exaust fan that comes on the side. I dont have the case yet, but im expecting it for christmas, and if I dont get it I'll buy it myself.