I chose the 80mm fans just to be different. I thought they also filled the available space well. The particular fans in question are Cooler Master R4-SPS-20AK-GP. You can see the full specs on NewEgg but they are basically 24CFM with 20dBA at 2,000 RPM. I was leaning more in favor of quiet versus efficient. I totally agree about the CPU cooler and I've been looking at different LGA 775 coolers. I was pondering possibly using a fanless one but I don't know how much heat that little Celeron 430 is going to put out. The drives in question are WDEARS 2TB Green drives. They're only running at 5,400 RPM so I don't think they'll overheat the case, even when I get 20 of them in there. I've currently got 2 drives and I'm going to move the 3rd out of my workstation once I get the data moved to my array.
Here are the fans in question:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103081