CMS 2GB (1X2GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core 2 Duo 2.8 24-Inch (Early 2008) - A40 at Amazon.com
How to Upgrade iMac RAM (20" and 24" Aluminum): EveryMac.com
Memory Upgrades for Apple iMac 2008 - Up to 6GB
Timetec 8GB KIT(2x4GB) Compatible for Apple DDR3 1067MHz / 1066MHz PC3-8500 CL7 for Mac Book,
A-Tech for Apple 6GB Kit (1x2GB + 1x4GB) DDR2 667MHz PC2-5300 200-pin SODIMM for MacBook (Late 2007, Early 2008, Early 2009), MacBook Pro (Mid 2007, Early 2008), iMac (Mid 2007) - Memory RAM Upgrade at Amazon.com