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
Upgrading 2008 iMac RAM - YouTube
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
How To: Adding RAM to iMac (2008) - YouTube
Install memory in an iMac - Apple Support
6GB (4GB & 2GB SODIMM Upgrade Kit) DDR2-800 for Apple iMac 2008 Core 2 Duo 8,1 - Newegg.com
Memory Upgrades for Apple iMac 2008 - Up to 6GB
Intel Core 2 Duo 6 GB RAM Apple Desktops & All-In-One Computers for sale | eBay