Here is the current CubieTruck FCluster.
There are six CubieTrucks. Each has an ARM Cortex A20 dual core processor with 2GB RAM, Gigabit Ethernet, 2 x USB 2 ports. It runs Debain Wheezy on a Class 10 32GB micro SDCard. Each CubieTruck has a 500GB HD attached via a SATA I interface. Control is via the tablet using Remote Desktop.
There's also a little Banana-pi which is being setup to drive the 10" touch screen.
This has recently been extended with several Raspberry Pi 2s with 4-core processors.