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 at Amazon.com
Installing additional SSD in Mid-2010 27" iMac
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com