I chose a Cooler Master HAF Stacker 935. When I started I only had 6 disks, so I put all 6 in the bottom trays and left the top empty. (It holds 9 with the default amount of trays/caddies)
I later added two drive bay thingies ($15 each) to the top and added another 6 disks.
A month or two ago, I bought a $60 "bottom" 915R and added two caddies to it. This gives me a total of 24 drive cages, for $160+$60 +4 X $15 = $280.
I started having temp issues, so I added fans top and bottom like here, but mine are external for better SATA cable clearance:
http://g-ecx.images-amazon.com/images/G/01/electronics/detail-page/B00FB45UNC_image_003.jpg
I keep it in my basement which is about 70F year round, and temps range from 27 (WD 5400 drives) to 37 (7200 RPM Hitachi)
194 Temperature_Celsius 0x0022 122 112 000 Old_age Always - 28
194 Temperature_Celsius 0x0022 123 109 000 Old_age Always - 27
194 Temperature_Celsius 0x0022 115 112 000 Old_age Always - 35
194 Temperature_Celsius 0x0022 116 106 000 Old_age Always - 34
194 Temperature_Celsius 0x0022 124 112 000 Old_age Always - 26
194 Temperature_Celsius 0x0022 118 104 000 Old_age Always - 32
194 Temperature_Celsius 0x0002 162 162 000 Old_age Always - 37
194 Temperature_Celsius 0x0002 176 176 000 Old_age Always - 34
194 Temperature_Celsius 0x0002 171 171 000 Old_age Always - 35
194 Temperature_Celsius 0x0002 166 166 000 Old_age Always - 36
194 Temperature_Celsius 0x0002 166 166 000 Old_age Always - 36
194 Temperature_Celsius 0x0002 171 171 000 Old_age Always - 35
194 Temperature_Celsius 0x0022 122 091 000 Old_age Always - 30
194 Temperature_Celsius 0x0022 119 084 000 Old_age Always - 31
194 Temperature_Celsius 0x0022 115 085 000 Old_age Always - 32
194 Temperature_Celsius 0x0022 115 087 000 Old_age Always - 32
194 Temperature_Celsius 0x0022 115 086 000 Old_age Always - 32
194 Temperature_Celsius 0x0022 119 090 000 Old_age Always - 31
194 Temperature_Celsius 0x0022 116 089 000 Old_age Always - 31
The 26 C drive is a failed drive that I haven't removed from the case yet.
