32GB (4x8GB) DDR3-1600MHz PC3-12800 Non-ECC UDIMM 2Rx8 Desktop Memory Module by NEMIX RAM at Amazon.com
Amazon.com: OWC 32.0GB (4X 8GB) DDR3 ECC PC10600 1333MHz SDRAM ECC, Compatible with Mac Pro (OWC1333D3W8M32K) : Everything Else
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
8GB DDR3 1600MHZ ECC/REG at Amazon.com
Crucial 8GB Single DDR3 1600 MT/s (PC3-12800) CL11 Unbuffered ECC UDIMM 240-Pin Server Memory CT102472BA160B at Amazon.com