Install RAM in a Macbook Pro - Kingston Technology - YouTube
Kingston Technology 4 GB Memory for Select Apple Imac's and Macbooks Single (Not a kit) 1066 MHz (PC3 8500) 204-Pin DDR3 SO-DIMM KTA- MB1066/4G at Amazon.com
Memory RAM Upgrade for Apple iMac 21.5-inch Mid 2011 4GB/8GB DDR3 SODIMM | eBay
How to install RAM in an iMac (video) - CNET
32.0GB OWC Memory Upgrade Kit For 2010-2011 Apple iMac
OWC 8GB (2 x 4GB) PC12800 DDR3L 1600MHz SO-DIMMs Memory Compatible with 2011-2015 iMac, 2011-12 Mac Mini, and 2011-2012 MacBook Pro (Non-Retina Display) Models (OWC1600DDR3S08S) at Amazon.com