32GB (4x8GB) DDR3-1600MHz PC3-12800 ECC UDIMM 2Rx8 1.35V Unbuffered Server Memory by NEMIX RAM at Amazon.com
Hynix HMT84GL7AMR4C-RD 32GB DDR3-1866 PC3-14900L 4Rx4 ECC Server Memory Module
32GB PC3L-10600L (1333Mhz) ECC Registered Load-Reduced Server Memory R – TechMikeNY
OWC 32GB (2 x 16GB) PC10600 DDR3 ECC-R 1333MHz DIMMs Memory Compatible with Mac Pro Early 2009 & Late 2010 'Nehalem' & 'Westmere' Systems and Early 2009 Xserve. (OWC85MP3S9M032K) at Amazon.com