INTEL S5520, Supermicro X8D, Gigabyte GA-7T - all available in several versions depending on your other needs.
again: strictly stick to the compatibility list of the mainboard when ordering memory!
be aware only 1 memory module per channel (= 3 per processor) allows 1333 - if you plan to insert more (6 per processor) you are fine with 1066 anyway.
christian
and remember: only a CRAY can run an endless loop in just three seconds.