Thanks for all the responses.
Yes, Fraggable, I'm familiar with those but I'm still not sure if they really do much to cool the drive... I guess every little bit helps.
Dangler, I love my case. There are a lot of times that I wish I had space for two optical drives, but I deal with it. I'm thinking of moving up to that uNeed case with the LCD on the front... it's pretty unique.
The interior space of my case is great for airflow, there are vents under the HDD cage, above the videocard, above the CPU, and at the rear of the case. Other than the Raptors, it runs pretty close to silent. The PSU is very quiet, I opted for a massive CoolerMaster copper finned/piped CPU cooler with a quiet 90mm fan pulling in air directly from the outside of the case. It keeps my S478 P4 3GHz running under 40C at all times - 23C at idle.
I bought a Arctic VGA Cooler for my ATI 9600 dual DVI 256MB card which keeps my GPU cool and near silent even at full blast, which also helps remove excess ambient air. Aside from the vibrations given off by my Raptors, the whole thing stays quiet and well below unsafe operating temps.
Last night I was messing around and took an older CPU turbine fan and mounted it to the side of my HDD cage to see what would happen. It definitely added a lot of fan whine to the system at full blast, but it did drop the temps on my HDDs between 5 and 10C. The entire HTPC is in an enclosed in an entertainment center, so I can't hear it with the door closed. I'm debating whether or not to keep it on there...
Meh.