A-Tech 16GB Kit (2x8GB) DDR3 1066MHz / 1067MHz PC3-8500 SODIMM RAM for Apple MacBook (13 inch, Mid 2010), MacBook Pro (13 inch, Mid 2010), iMac (27 inch, Late 2009), Mac Mini (Mid 2010) at Amazon.com
Memory Upgrades for Apple iMac 2011 Up to 32GB
apple-history.com / iMac (Late 2009)
Sold - 27" iMac Late 2009 // $295 - Boulder Mac Repair
My free iMac 27" (2009) core i7 2.8, 32GB, 1TB SSD High Sierra. only cost me a SSD and about an hour of time. : r/mac
Memory Upgrades for Apple iMac 2009 - Up to 32GB
A-Tech for Apple 2GB DDR3 1067MHz / 1066MHz PC3-8500 SODIMM Memory RAM Module for MacBook, MacBook Pro, iMac, Mac Mini - (Late 2008, Early 2009, Mid 2009, Late 2009, Mid 2010) Models at Amazon.com
Install memory in an iMac - Apple Support
Apple iMac (27-inch, unibody, 2009) review: Apple iMac (27-inch, unibody, 2009) - CNET
A-Tech 16GB (4 x 4GB) PC3-8500 DDR3 1066/1067 MHz RAM for iMac Late 2009 21.5-inch / 27-inch | 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
Review: Apple's 27" big screen iMac (late 2009) | AppleInsider