You might need to check the airflow in your case, the tempuratures do get up there. I'm loading up rivatuner right now and I'll get you some numbers for what I run in COD4 on the stock cooler.
As for aftermarket coolers I've used this: http://www.arctic-cooling.com/vga2.php?disc=1&idx=40
They don't sell that one anymore, but they have a new product that should fit. http://www.arctic-cooling.com/vga2.php?idx=91 http://www.newegg.com/Product/Produc...82E16835186001
I just checked at it's running about 66C idle and I topped out around 95C using the stock cooler. I know that other cooler I use on another card kept it to around 80C, but I also have better airflow in the other pc.