On March 6, 2012, Intel finally released the Xeon E5 processor family, (aka the Sandy Bridge-EP). Sandy Bridge is a Tock release for Intel, and as such, it represents a huge jump in both performance and power efficiency over the previous 32nm Westmere-EP (which was no slouch). It is initially available for two socket servers (the E5-2600 series), but it will also be available for four socket servers in the future (the E5-4600 series). Sometime in 2013, we will see the 22nm Ivy Bridge-EP, which will be a Tick release that will be socket compatible with Sandy Bridge-EP.
Make no mistake, Sandy Bridge-EP is the processor that you want for the vast majority of SQL Server workloads. The main exception would be a case where you really need more than six PCI-E 3.0 slots, and you need more than 24 memory slots (with either 384GB or 768GB of RAM, with 16GB or 32GB DIMMs, respectively).
Here are a number of relevant articles and reviews about the Sandy Bridge-EP:
Intel® Xeon® Processor E5-2690 (Intel specification sheet for Xeon E5-2690)
The Xeon E5-2600: Dual Sandy Bridge for Servers (Anandtech review of Xeon E5-2690)
Intel rolls out Xeon E5-1600 and E5-2600 CPUs (CPU-World news story about Xeon E5 release)
Sandy Bridge-EP Review (David Kanter review of Sandy Bridge-EP)
Sandy Bridge-EP Launches (David Kanter article about Sandy Bridge-EP launch)
Sandy Bridge for Servers (David Kanter article about Sandy Bridge-EP architecture)
Intel Xeon E5-2690 Sandy Bridge-EP Performance Revealed (Tom’s Hardware article about Sandy Bridge-EP)
IBM System x3650 M4 (First Xeon E5-2690 TPC-E Benchmark Submission)