iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
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
iMac Intel 20" Mid 2007 EMC 2133 - used original spareparts for Macs
A-Tech for Apple 1GB DDR2 667MHz PC2-5300 200-pin SODIMM for MacBook, MacBook Pro, iMac, Mac Mini - (Early/Mid/Late 2006, Mid/Late 2007, Early 2008, Early 2009) - Memory RAM Module at Amazon.com
4GB 2 X 2GB DDR2 Memory for iMac 7,1 Mid 2007 20" inch 24" inch Intel Core 2 Duo 2.4GHz PC2-5300 667MHz 200 pin SODIMM (PARTS-QUICK) at Amazon.com
Review: Apple's new 24-inch iMac (aluminum) | AppleInsider
Install memory in an iMac - Apple Support
Apple A1225 24-inch iMac 7.1 Core 2 Duo 2.4GHz 320GB HD 2GB RAM Mid-2007 MA878LL | RecycledGoods.com
Memory Upgrades for Apple iMac 2007 - Up to 6GB
Install memory in an iMac - Apple Support
MemoryMasters 6GB (4GB + 2GB Memory Upgrade Kit) Memory RAM for Apple iMac 2007 7,1 at Amazon.com
CMS 4GB (2X2GB) DDR2 5300 667MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac (Mid 2007) Pc2-5300 - A37 at Amazon.com
Memory Upgrades for Apple iMac 2007 - Up to 6GB
6GB Memory for 2007-2008 MacBook Pro, MacBook, and iMac