Apple iMac 21.5-inch Late 2009 - 3.33GHz Core 2 Duo Desktop RAM Memory | Kingston
8GB -2x4GB Memory Ram Upgrade 20" Apple iMac 9.1 2.66GHz Core 2 Duo Early 2009 | eBay
Install memory in an iMac - Apple Support
Timetec 16GB KIT(4x4GB) Compatible for Apple DDR3 1067MHz / 1066MHz PC3-8500 CL7 Dual Rank for iMac (Late 2009 21.5-inch / 27-inch) SODIMM Memory MAC RAM Upgrade for iMac 10,1 and iMac 11,1 at Amazon.com
How to Upgrade Memory in a Late 2009 21.5-inch or 27-inch iMac - YouTube