Amazon.com: OWC 32 GB (1x 32GB) PC3-10600 1333MHz DDR3 ECC-R SDRAM Memory Upgrade Kit Compatible with 2013 Mac Pro (OWC1333D3MPE32G) : Everything Else
G.Skill Ripjaws X Series 16 GB (2 x 8 GB) 240-Pin SDRAM (PC3-12800) DDR3 1600 CL10-10-10-30 1.50V Dual Channel Desktop Memory Model F3-12800CL10D-16GBXL at Amazon.com
Axiom Memory 16GB DDR3 SDRAM Memory Module 647901-B21-AX at Amazon.com
G.SKILL Ripjaws X Series 8GB (2 x 4GB) Desktop Memory, 240-Pin DDR3 SDRAM, 1600 MHz, PC3 12800 (F3-12800CL9D-8GBXL) 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
G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model (F3-12800CL9D-8GBRL) at Amazon.com
HPE RAM Memory 1 x 8GB DDR4 SDRAM 8 DDR3 2400 SDRAM 759934-B21 at Amazon.com