I suggest 120mm fans with 80-CFM or above. But first what case do you have? One fan you installed to OC your video card? I wouldent count on just one fan to keep my system from burning out.
Try this site out, go to fans and check out their sizes.
Personally i suggest a new Heatsink/CPU fan. For you Video Card i suggest a VGA Heatsink, with a Dual PCI Fan pointed above at your AGP. Something like these:
For a PCI cooler, i would order it, then see what size fans it holds, and replace them with the best you can find for that size. Heatsinks and fans always go good togather.