How to Upgrade Memory in a Late 2009 21.5-inch or 27-inch iMac - YouTube
Memory Upgrades for Apple iMac 2009 - Up to 32GB
Late 2009, 27 inch iMac can use 32 GB of 1333 MHz RAM, beyond what Apple says - YouTube
A-Tech 32GB (4 x 8GB) PC3-8500 DDR3 1066/1067 MHz RAM for iMac Late 2009 27- inch (Quad-Core i5/i7) | 204-Pin SODIMM Max Memory Upgrade Kit at Amazon.com