EVGA have released a dual Nehalem Xeon board that they claim is overclockable, comes with a full 12 DIMM slots and seven x16 PCIe slots!
http://www.bit-tech.net/hardware/motherboards/2010/01/27/evga-w555-dual-xeon-motherboard/1
http://www.bit-tech.net/hardware/motherboards/2010/01/27/evga-w555-dual-xeon-motherboard/1