Komputerbay 16GB (4 X 4GB) DDR3 DIMM (240 pin) 1333Mhz PC3 10600 / PC3 10666 16 GB KIT at Amazon.com
48GB (3X 16GB) Matched Pair 1333MHz 240-Pin SDRAM DIMM DDR3 (PC10600) Memory Upgrade Kit for PC Desktops, Mac Pro 'Nehalem' & 'Westmere' (OWC1333D3X9M048) at Amazon.com
Xtremeram Apple Compatible Memory Module 8GB 1333MHz DDR3 (PC3-10600) - 2x4GB at Amazon.com