HP 8GB (1 x 8 GB) 1333 MHz (2Rx4 PC3L-10600R) 240-pin DIMM DDR3-1333 Memory Module (647897-B21) at Amazon.com
8GB DDR3 SDRAM Memory Module at Amazon.com
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