Cluster Monkey was talking recently about the new Appro workstation:
Appro International has just announced the XtremeWorkstation. — a deskside workstation that can hold up to four (4) AMD Opteron Processors. So let’s do some math. With four sockets, that is eight cores in one box, and when the Barcelona quad-core comes out, that is 16 cores in one box. Remember your first 16 node cluster? Now you can get 16 cores in a single desk side SMP system (Symmetric Multi-Processing).
More at their web site.