Here is the all things about dual processor motherboards even for quad processor motherboards, hope you like it and it's still counting
List of dual processor motherboard products (so far) :

1. Introducing about dual processor motherboard
2. EVGA SR3 X79 : dual socket motherboard for Intel socket 2011
3. Asus Z8NA-D6C : Socket 1366 Motherboard for Dual Intel Xeon
4. Dual Processor Gaming Motherboard : Samples Mobo's
5. Dual Processor Motherboard AM3 : Intro
6. Dual Quad Core Processor Motherboard : Intro
7. Dual Processor Motherboard for Intel i7 : Intro
8. Asus KCMA-D8 : Dual AMD Opteron 4100
9. EVGA Showing The EVGA SR-X Dual Intel LGA2011

Still counting/updating.