Cooler Master Stacker STC-T01
It takes all ATX mainboards you'll ever throw at it, it can be converted to BTX without much fuss, it takes two power supplies. The list goes on. I mentioned that the Stacker's size would afford its creators options for new and useful internal case cooling schemes, if they were smart. Cooler Master are smart, the X-Flow fan really doing the job in terms of keeping the mainboard area cool with the minimum of created noise.