4x Drillbit 8-boards (bitfury chips) @ 81GH/s. They can overclock to 88GH/s with some fiddling around.

CPU: Intel Celeron G530 @ 1.6GHz
Mobo: Gigabyte H77M-D3H
RAM: 1x4GB Kingston DDR3 @ 1066MHz @ 1.2v
HDD: Intel X25-M G2 80GB
Case: Antec P182
PSU: Antec CP-850
Fans: 4x Scythe GT 1850RPM (two on each pair of 8-boards for extra airflow), 1x 140mm 1200RPM for support, and 1x 120mm 1300RPM for exhaust
OS: Windows 7 Ultimate 64-bit