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
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
OWC 6GB (2GB + 4GB) PC8500 DDR3 1066MHz SO-DIMMs Memory Compatible with Late 2008, Early 2009, Early 2010 MacBook, MacBook Pro Unibody Models, 2009/2010 Mac Mini, 2009 iMac Models at Amazon.com
How to Upgrade Mac Pro Memory (Early 2009/MacPro4,1): EveryMac.com
8GB kit (2x4GB) DDR3 1066 SODIMM for Apple iMac (2009), MacBook Pro (2 – Aplus Technology
iMac (2009) RAM & Storage Upgrades
4GB NEMIX RAM Memory for Apple iMac Early & Mid 2009 System Specific Memory - Newegg.com