CMS 1GB (1X1GB) RAM Memory 4 Apple iMac "Core 2 Duo" 2.4 20-Inch Early 2008 - Walmart.com
SOLVED: How can I upgrade my early 2008 24" iMac? - iMac Intel 24" EMC 2134 and 2211 - iFixit
iMac Memory for Model 17.1 | DDR3 1866MHz | Late 2015 | RAMJET.com
CMS 4GB (1X4GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core 2 Duo 2.4 20-Inch Early 2008 - A42 at Amazon.com
OWC 8GB PC3-12800 DDR3L 1600MHz SO-DIMM 204 Pin CL11 Memory Module Upgrade Compatible with iMac, Mac Mini, and MacBook Pro (OWC1600DDR3S8GB) at Amazon.com
RAM upgrade considerations for iMac systems - CNET
CMS 4GB (1X4GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core 2 Duo 2.4 20-Inch Early 2008 - A42 at Amazon.com
Amazon.com: OWC 8GB (2 x 4GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S08P) : Everything Else