Here's a 6600GT that looks a little different from what we've seen before. Legion Hardware have a review of ASUS' silent 6600GT.
While the large red aluminum heatsink is designed to passively cool the front memory chips as well as the GPU, it is not the last line of defense against heat. There is a long heatpipe that runs through the core of this red heatsink and is bent at a 90 degree angle at the top. This pipe then connects to another 50 odd thin copper fins. These fins provide even greater cooling power for the Extreme N6600GT Silencer. ASUS has been very clever with their implementation of these top mounted fins.