my designs are quite simplistic..Basically air in the front and out the back.. the easier/faster it passes through the case the better.
Try to make the airflow as straight as possible and keep as much wiring/junk out of the way as possible.
My 9600GTs use Accelero Coolers and run in the 20-30C range and are silent.
http://www.newegg.com/Product/Produc...82E16835186016
your main prob is your intake (front of the case is flat/solid so air needs to come from a small slot in the bottom)
Here is a very good case take a look at how air goes in and out
http://www.newegg.com/Product/Produc...82E16811112099
some of its really good points are
top vent (helps to equalize air pressure and allow heat to exit)
front face is perforated to allow air to enter
rear fan mount has no little holes in its center to restrict air
alum gets rid of heat better\
HDD rack is in good place to cool Hdds
One of the cool things about the 9800GTX+s is they are 55nm cores so they all run cooler than the reg 9800GTXs.
That Asus cooler looks very nice (low profile and fins run front to back)