iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
iMac Intel 21,5" Late 2009 EMC 2308 - used original spareparts for Macs
Timetec 8GB KIT(2x4GB) Compatible for Apple DDR3 1067MHz / 1066MHz PC3-8500 CL7 for Mac Book, Mac Book Pro, iMac, Mac Mini (Late 2008, Early/Mid/Late 2009, Mid 2010) SODIMM Memory MAC RAM Upgrade
CMS 4GB (1X4GB) DDR3 8500 1066MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core 2 Duo 3.06 21.5-Inch (Late 2009) - A34 at Amazon.com